Ablative Plastic: Material that absorbs heat (with low material loss and char rate) through a decomposition process (pyrolysis) that takes place at or near the surface exposed to the heat.

ABS: Acrylonitrile Butadiene Styrene (Thermoplastic Resin).

Abrasion: Wearing away by friction. Glass is highly resistant to abrasion by other materials, but can be damaged through contact with itself. A lubricant is used during processing and fabrication to prevent abrasion.

Accelerated Test: Procedure in which conditions are increased in magnitude to reduce the time required to obtain a result. To reproduce in a short time the deteriorating effect obtained under normal service conditions.

Accelerator (Promoter): A highly active oxidizing agent suspended in a liquid carrier used in conjunction with a catalyst to produce internal heat in a liquid plastic to cure it. Examples are diethylaniline, cobalt naphthanate and cobalt octoate.

Acetone: (Styrene solubility) - The percentage of the sizing on the glass fiber that is dissolved off the strand in acetone (or styrene) after soaking in the solvent.

Acoustic Emission: Measure of integrity of a material, as determined by sound emission when a material is stressed. Ideally, emissions can be correlated with defects and/or incipient failure.

Acrylic: Thermoplastic polymer made by the polymerization of esters of acrylic acid and its derivatives.

Activator: See Accelerator.

Actual End Count: The number of bundles or splits that are actually counted in one doff of roving. (This is less than the theoretical end count due to splitting efficiencies of less that 100%).

Addition polymerization: Chemical reaction in which simple molecules (monomers) are added to each other to form long-chain molecules (polymers) without forming byproducts.

Additive: Any number of materials used to modify the properties of polymer resins, such as plasticizers, initiators, light stabilizers and flame-retardants.

Adhesive: Substance capable of holding two materials together by surface attachment. Adhesive can be in film, liquid, or paste form.

Admixture: Addition and homogeneous dispersion of discrete components, before cure.

Aggregate: Hard, coarse material usually of mineral origins in composite tools. Also used in flooring or as a surface medium.

Aging: Effect on materials of exposure to the environment. The process of exposing materials to an environment for an interval of time.

Air-bubble: Void air entrapment within and between plies of reinforcement or within a bond line or encapsulated area; localized, non-interconnected, spherical in shape.

Air Splice: The coupling between two roving doffs which is made by a jet of air entwining/snarling the two strands together. The air splice is used instead of a knot.

Air Vent: Small outlet to prevent entrapment of gases in a molding or tooling fixture.

Alligatoring: Visible cosmetic defect in exposed gel coat which looks like wrinkled or alligator skin.

Alloy: In plastics, a blend of polymers or copolymers with other polymers or elastomers under selected conditions.

Ambient: Surrounding environmental conditions, such as pressure, temperature, or relative humidity.

Angle-Ply Laminate: Laminate having fibers of adjacent plies oriented at alternating angles.

An Isotropic: Exhibiting different properties when tested along axes in different directions. See An isotropic laminate and Isotropic

An Isotropic Laminate: One in which the properties are different in different directions.

Antioxidant: Substance that, when added in small quantities to resin, prevents oxidative degradation and contributes to the maintenance of its properties.

Antistatic Agents: Agents that, when added to a molding material or applied to the surface of a molded object, make it more conducting, thus hindering the fixation of dust or the buildup of electrical charge.

Arimid: Type of highly oriented organic material derived from polyamide but incorporating aromatic ring structure. Used primarily as a high-strength, high-modulus fiber. Kevlar and Nomex are example of arimid.

Arc Resistance: Ability to withstand exposure to an electric voltage. The total time in seconds that an intermittent arc may play across a plastic surface without rendering the surface conductive.

Ash Content: Proportion of the solid residue remaining after a reinforcing substance has been incinerated (charred or intensely heated).

Aspect Ratio: Ratio of length to diameter of a fiber.

A-Stage: Early stage in the polymerization reaction of certain thermosetting resins (especially Phenolic) in which the material, after application to the reinforcement, is still soluble in certain liquids and is fusible. Also called resole. See B-Stage and C-Stage

ASTM: American Society of Test Methods.

Autoclave: Closed vessel for conducting and completing a chemical reaction or other operation, under pressure and heat.

Autoclave Molding: Process in which, after lay-up, winding, or wrapping, and entire assembly is placed in a heated autoclave, usually 50 to 200 psi. Additional pressure permits higher density and improved removal of volatiles from the resin. Lay-up usually vacuum bagged with a bleeder and release cloth.

Autosprue™: Automatic gate at the inlet sprue of the mold which eliminates the need to remove the resin supply during the injection process for flushing. See: Autosprue

Axial Winding: In filament-wound reinforced plastics, a winding with the filaments parallel or at a small angle to the axis (0° helix angle).

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Bagging: Applying an impermeable layer of film over an uncured part and sealing the edges so that a vacuum can be drawn.

Bag Molding: Process in which the consolidation of the material in the mold is affected by the application of fluid or gas pressure through a flexible membrane.

Balanced Construction: Equal parts of warp and fill in fiber fabric. Construction in which reactions to tension and compression loads result in extension or compression deformations only, and in which flexural loads produce pure bending of equal magnitude in axial and lateral directions.

Balanced Laminate: Composite laminate in which all laminate at angles of 0° and 90° occur only in + or - pairs (not necessarily adjacent) and are symmetrical around the centerline.

Ball: See Roving

Band Width: In filament winding, the width of the reinforcement as it is applied to the mandrel.

Barcol-Shore Rockwell Hardness: This is a property of material which describes its ability to be indented. The Rockwell method for measuring hardness forces a steel point into the material and then measures the penetration of the point. The different letters in the Rockwell reading describe the shape of the point and the load applied during the test. Units - Rockwell units with the appropriate suffix letter. The letter and number cannot be separated. Higher numbers with the same letter indicate harder materials. Harder materials have more resistance to penetration by another substance.

Bare Glass: The glass as it flows from the bushing in fiber form, before a binder or sizing is applied.

Batch Oven: Large temperature-controlled oven, used to heat-clean rolls of glass fiber fabric.

Batt: Felted fabrics. Structures built by the interlocking action of compressing fibers, without spinning, weaving, or knitting.

Beam: A spool, on which is wound a number of parallel ends of singles or plied yarns, for use in weaving or similar processing operations.

Beaming: Operation in which many ends of yarn from a creel are combined on a section beam.

Bearing Strength: Maximum bearing stress that can be sustained. Also, the bearing stress at that point on the stress-strain curve where the tangent is equal to the bearing stress divided by n% of the bearing hole diameter.

Bearing Stress: Applied load in pounds divided by the bearing area. Maximum bearing stress is the maximum load in pounds sustained by the specimen during the test, divided by the original bearing area.

Bed: The result of the chopping operation. A mat of chopped glass fibers that is deposited onto a layer of resin mix on a carrier film under the chopper.

Bias Fabric: Warp and fill fibers at an angle to the length of the fabric.

Biaxial Load: Loading condition in which a laminate is stressed in two different directions in its plane. A loading condition of a pressure vessel under internal pressure and with unrestrained ends.

Biaxial Winding: In filament winding, a type of winding in which the helical band is laid in sequence, side by side, with crossover of the fibers eliminated.

Bi-directional: Reinforcing fibers that are arranged in two directions, usually at right angles.

Bi-directional Laminate: A reinforced plastic laminate with the fibers oriented in two directions in its plane. A cross laminate.

Binder: A coating applied to the surface of a chopped glass mat or preform which is then cured. The binder holds the previously sized glass bundles or ends together in the roving operation into a stable shape or form.

Birdnest: A large collection of continuous glass bundles which is tangled up and will not run through the guide eye into roving creel. In the field, a large tangled collection of roving which does not run through the tube or guide eyes to the chopper.

Bismaleimide (BMI): Type of polyamide that cures by an addition rather than a condensation reaction, thus avoiding problems with volatiles formation, and which is produced by a vinyl-type polymerization of a pre-polymer terminated with two maleimide groups. Intermediate in temperature capability between epoxy and polyamide.

Blade Packing: Glass bundles or chopper fuzz which build up and pack between the blades of a chopper. This blade packing can cause poor choppability. If it falls off, it usually does not wet-through, and this can cause blisters or porosity.

Blanket: Fiber or fabric plies that have been laid up in a complete assembly and placed on or in the mold all at one time (flexible bag process). Also, the form of bag in which the edges are sealed against the mold.

Bleeder Cloth: Woven or non-woven layer of material used in the manufacture of composite parts to allow the escape of excess gas and resin during cure. The bleeder cloth is removed after the curing process and is not part of the final composite.

Blister: Flaw either between layers of laminate or between the gel coat film and laminate.

BMC: Bulk Molding Compound (Thermoset).

Bobbin: The spool or shipping package on to which textile yarns are wound.

Bond Strength: Amount of adhesion between bonded surfaces. The stress required to separate a layer of material from the base to which it is bonded, as measured by load/bond area.

Boron Fiber: Fiber produced by vapor deposition of elemental boron, usually onto a tungsten filament core, to impart strength and stiffness.

Braid/Braider: A narrow tubular or flat fabric produced by intertwining a single set of yarns according to a definite pattern.

Breakup: See Dispersion.

Breathing: Opening and closing of a mold to allow gas to escape early in the molding cycle. Also called "degassing"; sometimes called "bumping" in Phenolic molding.

Bridging: Condition in which fibers do not move into or conform to radii and corner during molding, resulting in voids and dimensional control problems.

Broad Strand: See Wides or Matchsticks.

Broken Strand: See Broken End.

Broken End: In the roving operation, a broken or severed strand (bundle) which causes the forming cake to stop running.

Broken Fibers: See Fuzz.

B-Stage: Intermediate stage in the reaction of certain thermosetting resins in which the material softens when heated and is plastic and fusible buy may not entirely dissolve or fuse. Also called "resistol" or "resitol." The resin in an uncured prepreg or premix is usually in this stage.

Buckling (Composite): Mode of failure generally characterized by an unstable lateral material deflection due to compressive action on the structural element involved.

Buildup: Glass bundles or chopper fuzz which collect on the chopper, cot, static bars or machine frame.

Bulk Molding Composite (BMC): Thermosetting resin mixed with short strand reinforcement, filler, and so on, into a viscous compound for compression or injection molding.

Bundle: A discrete collection of many parallel glass filaments. A collection of individual filaments, a sub-strand.

Bushing: Plate with holes through which molten glass is pulled to produce glass fibers.

Bushing Tip: Small tapered protrusions on the bottom of bushings each containing an orifice through which molted glass flows, from which continuous filaments are drawn.

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Cabled Yarn: Yarn that is plied more than once; yarn made by plying two or more previously plied yarns.

Carbon: Element that provides the backbone for all organic polymers. Graphite is a more ordered form of carbon. Diamond is the densest crystalline form of carbon.

Carbon-Carbon: Composite material consisting of carbon or graphite fibers in a carbon or graphite matrix.

Carbon Fiber: Fiber produced by the pyrolysis of organic precursor fibers, such as rayon, polyacrylonitrile (PAN), and pitch, in an inert environment.

Carding: The process of untangling and partially straightening fibers by passing them between two closely spaced surfaces which are moving at different speeds, and at least one of which is covered with sharp points, thus converting a tangled mass of fibers to a filmy web.

Casting: Process of pouring a mixture of resin, fillers and/or fibers into a mold as opposed to building up layers through lamination. This technique produces different physical properties from laminating.

Catalyst (Hardener): A substance which markedly speeds up the cure of a compound by decomposing in the presence of a promoter to release an active oxygen radical. Catalyst content can vary from 0.2% to 2.0% with higher catalyst levels giving faster gel times. Examples are methyl ethyl ketone peroxide, benzoyl peroxide.

Catastrophic Failures: Totally unpredictable failures of a mechanical, thermal, or electrical nature.

Catenary: A consolidated group of individual strands which, when checked between two fixed points of length, exhibit strands of different lengths. The resulting curve between fixed points of the inextensionable material is defined as catenary. The amount of catenary is measured by the distance between the topmost and lowermost strands when stretched between two fixed points.

Caul Plates: Smooth metal plates, free of surface defects, the same size and shape as a composite lay-up, used immediately in contact with the lay-up during the curing process to transmit normal pressure and temperature, and to provide a smooth surface on the finished laminate.

Cavity: Space inside a mold in which a resin or molding compound is poured or injected. The female portion of the mold. That portion of the mold that encloses the molded article (often referred to as the die). Depending on the number of such depressions, molds are designated as a single cavity or multiple cavity.

Cell: The vertical plane of doffs on a pallet. A pallet may be constructed for 4- or 12-end run-out depending on application.

C-Glass: Glass with a soda-lime-borosilicate composition that is used for its chemical stability in corrosive environments.

Chalking: Surface phenomenon indicating degradation of a cosmetic surface. Chalking is a powdery film which appears lighter than the original color.

Chemical Size: A surface finish applied to the fiber that contains some chemical constituents other than water.

Choppability: The ease of chopping/cutting the glass fibers to a uniform length.

Clamping Pressure: In injection molding and transfer molding, the pressure that is applied to the mold to keep it closed in opposition to the fluid pressure of the compressed molding material.

Cloth: Fiberglass reinforcement made by weaving strands of glass fiber yarns.

Clump: A group of chopped bundles of glass fibers which has collected on the SMC machine and then fallen into the bed of glass. The clump produces areas of high glass content which may not wet-through.

Coefficient of Thermal Expansion (CTE): How much a material shape will change for each degree of temperature change.

Cold Flow: The distortion that takes place in materials under continuous load at temperatures within the working rage of the material without a phase or chemical change.

Collet: A spool on which the gathered strands from the bushing are wound for further processing.

Compaction: The application of a temporary vacuum bag and vacuum to remove trapped air and compact the lay-up; also in SMC machines for removal of air prior to roll-up.

Compatibility: The ability of two or more substances combined with one another to form a homogeneous composition of useful plastic properties; for example, the suitability of a sizing or finish for use with certain general resin types.

Composite: Chemical or mechanical bonding of dissimilar materials such as glass fiber and polyester resin, whose cumulative properties are superior to the individual materials.

Composite Material: A combination of two or more materials (reinforcing elements, fillers, and composite matrix binder). The constituents retain their identities; that is, they do not dissolve or merge completely into one another although they act in concert. Normally, the components can be physically identified and exhibit an interface between one another.

Compounder: Manufacturer who mixes a polymer, fillers, additives and glass fibers, and sells the resulting pellets for injection molding.

Compression Molding: A process where a mold is open when the material is introduced and shapes the material by the pressure of closing and by heat.

Compressive Modulus: Ratio of compressive stress to compressive strain below the proportional limit. Theoretically equal to Young's modulus determined from tensile experiments.

Compressive Strength: This number describes how much of a nonmoving load a bar can take before it is crushed. Units are normally thousands of pounds per square inch. (103 psi) - Mega Pascals (mPa). Higher numbers indicate stronger materials which can withstand a heavier load before they break.

Condensation Polymerization: A chemical reaction in which two or more molecules combine, with the separation of water or some other simple substance.

Conductivity: Reciprocal of volume resistivity. The electrical or thermal conductance of a unit cube of any material (conductivity per unit volume).

Conformability: Ability of the mat to conform to difficult shapes without causing wrinkles or leaving excessively resin-rich or glass-rich radii, which may craze.

Contact Molding: Refers to the use of a single or open mold onto which layers of polymer and reinforcement materials can be applied. Contact molding is characterized by one finished cosmetic side. Cure is either at room temperature using a catalyst-promoter system or by heating in an oven, without additional pressure.

Continuous Filaments: Filaments that extend substantially throughout the length of the yarn.

Continuous Heat Resistance: This is the maximum temperature the material should be subjected to in a continuous application. Below this temperature the material is acceptable. Above this temperature the material may decompose, melt, or otherwise fail in an application. Units - degrees Fahrenheit (°F)- degrees Centigrade (°C). Higher numbers mean that the material can be used continuously at higher temperatures.

Continuous Laminating: Process for forming panels and sheeting in which fabric or mat is passed through a resin bath, brought together between covering sheets, and passed through a heating zone for cure. Squeeze rolls control thickness and resin content as the various plies are brought together.

Continuous Rovings: Rovings supplies in a package that allows for continuous processing.

Continuous Strand: Fiberglass mat of very long individual fibers with a regular crossed pattern loosely held together with a binder.

Copolymer: A resin produced by copolymerization, the process where unlike molecules are arranged in alternate sequence in a chain.

Core: A low-density material used between two FRP skins. Examples of core materials are end-grain balsa wood, urethane foam, PVC foam and various honeycomb materials. The central member, usually foam or honeycomb, of a sandwich construction to which the faces of the sandwich are attached or bonded. The central member of a plywood assembly. A channel in a mold for circulation of heat transfer media. A device on which prepreg is wound.

Coronizing: Continuous heat cleaning and weave setting.

Corrosion Resistance: The ability of a material to withstand contact with ambient natural factors or those of a particular artificially created atmosphere, without degradation or change in properties. For metals, this could be pitting or rusting; for or organic materials, it could be crazing.

Coupling Agent: Any chemical substance designed to react with both the reinforcement and matrix phases of a composite material to form or promote a stronger bond at the interface.

Crazing: Cracking of gel coat or resin due to stress. Region of ultra-fine cracks, which may extend in a network on or under the surface of a resin or plastic material. May appear as a white band. Often found in a filament-wound pressure vessel or bottle.

Creel: Glass Fiber Manufacturing - A framework used to hold forming cakes so they can be wound or roved into roving doffs. Creels generally hold 10 to 33 forming cakes which are replaced randomly as they run out as doffs are roved. Composite Fabrication - The area where the pallets of roving are placed and "threaded up" through metal tubes or guide eyes to a chopper.

Creep: The slow movement of a plastic material with time.

Creep, Rate of: Rate of the slope of the creep-time curve at a given time. Deflection with time under a given static load.

Crosslinking: The setting up of chemical links between molecule chains. This occurs in all thermosetting resins. Styrene monomer is a crosslinking agent in polyester resins.

C-Stage: The final stage in the reaction of certain thermosetting resins in which the material is practically insoluble and infusible.

CTE: see Coefficient of Thermal Expansion.

Cure: The crosslinking or total polymerization of the molecules of the resin which alters the properties of the material and changes it from a liquid into a solid.

Cure Cycle: The time/temperature/pressure cycle used to cure a thermosetting resin system or prepreg

Cure Time: The time required for the liquid resin to reach a cured or fully polymerized state after the catalyst has been added.

Curing Agent: A catalytic or reactive agent that, when added to a resin, causes polymerization. Also called hardener.

Cut Ends on Doff: Severed ends on the doff which generally are caused by abrasion during shipping or by careless use of a knife when the package is removed from the pallet.

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Damping: The decay with time of the amplitude of free vibrations of a specimen.

DAP: Diallyl Phthalate (Thermoset Resin).

Daylight: The distance, in the open position, between the moving and fixed tables or the platens of a hydraulic press. In the case of a multi-platen press, daylight is the distance between adjacent platens. Daylight provides space for removal of the molded part from the mold.

Deflashing: A finishing technique used to remove the excess, unwanted material (flashing) on a plastic molding.

Delamination: Separation of composite layers, either local or covering a wide area. Can occur in the cure or subsequent life.

Denier: A direct numbering system for expressing linear density, equal to the mass in grams per 9000m of yarn, filament, fiber, or other textile strand.

Density: This is defined as the weight of a material per unit volume. Units - pounds per cubic inch (lb/cu in) grams/cubic centimeter. Higher numbers indicate heavier materials. Note: Density in lbs/cu in, and Specific Gravity are conveniently related by the following ratio:

Density (LB/cu in) Density (gr/cu cm)
-------------------- = 0.0361 -------------------- = 0.9975
Specific Gravity Specific Gravity
Density, Fiber:
Mass per unit volume of the solid matter of which a fiber is composed, measured under specified conditions.

Dielectric: A nonconductor of electricity. The ability of a material to resist the flow of an electrical current.

Dielectric Constant: The ratio of the capacitance of an assembly of two electrodes separated solely by a plastic insulating material to its capacitance when the electrodes are separated by air.

Dielectric Heating: The heating of materials by dielectric loss in a high-frequency electrostatic field.

Dielectric Strength: This is an electrical property and gives an indication of how well the material acts as an electrical insulator. It describes how much of an electrical voltage can be built up on one side of the material before it is communicated to the other side. Units - Volts per mil of thickness (volts/mil). Higher numbers indicate materials which are better insulators. C means that the material conducts electricity and therefore has no dielectric strength.

Dimensional Stability: Ability of a plastic part to retain the precise shape to which it was molded, cast, or otherwise fabricated.

Direct-Sized Yarn: Specially formulated sizings on textile yarns that allow them to be resin compatible.

Dispersion: The degree to which the roving separates into discrete bundles after being chopped. Good dispersion is characterized by a bed of bundles which are uniform in width. Poor dispersion is characterized by a wide distribution in the widths of various bundles in the bed. Poor dispersion can cause poor wet-through and wet-out.

Distortion: Change in shape from that which is intended. Symptomatic of laminating difficulties, curing problems, tooling problems or resin shrinkage.

Doctor Blade or Bar: A straight piece of material used to spread resin, as in application of a thin film of resin for use in hot melt prepreg or for use as an adhesive film. Also called paste metering blade.

Doff: See Roving Doff

Doff Collapse: The failure of the roving doff to maintain its shape and stability during run-out or storage. Doff collapse generally occurs when there is only a 1/2" to 1/4" ring of roving left from the original doff.

Draft: The taper or slope of the vertical surfaces of a which allow removal of molded parts.

Dry Loft: Height of the bed of chopped fibers.

Dwell: A pause in the application of pressure or temperature to a mold, made just before it is completely closed, to allow the escape of gas from the molding material.

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E Glass: A family of calcia-alumina-silicate glasses which has a certified chemical composition and which is used for general purposes and most electrical applications. (ASTM D578-90.)

Elasticity: That property of materials by virtue of which they tend to recover their original size and shape after removal of a force causing deformation.

Elastic Limit: The greatest stress a material is capable of sustaining without permanent strain remaining after the complete release of the stress. A material is said to have passed its elastic limit when the load is sufficient to initiate plastic, or non-recoverable, deformation.

Elastomer: A material that substantially recovers its original shape and size at room temperature after removal of a deforming force.

Elongation: As mentioned under tensile modulus, when a bar is pulled it gets longer. The elongation tells how much longer it gets before it breaks.

Encapsulating: Completely surrounding an object with resin or a fiber resin composite. Sometimes used specifically in reference to the enclosure of capacitors or circuit board modules.

End: A single bundle of filaments.

End count: An exact number of ends supplied on a ball of roving.

Environment: The aggregate of all conditions (such as contamination, temperature, humidity, radiation, magnetic and electric fields, shock, and vibration) that externally influence the performance of an item.

Epoxy: A polymerizable thermoset polymer containing one or more epoxide groups and curable by reaction with amines, alcohols, phenols, carboxylic acids, acid anhydrides, and mercaptans. An important matrix resin in composites and structural adhesive. Epoxies generally have higher physical properties than polyester resins. They are also more costly and difficult to process, and less able to withstand sunlight.

Even Tension: The process whereby each end of roving is kept in the same degree of tension as the other ends making up the ball of roving.

Exothermic Heat: Heat given off during a polymerization reaction by the chemical ingredients as they react and the resin cures.

Extend: To add fillers or low-cost materials in an economy producing endeavor. To add inert materials to improve void-filling characteristics and reduce crazing.

Extenders: Low-cost materials used to dilute or extend high-cost resins without extensive lessening of properties.

Extruder: Machine that pushes molten plastic through small holes to form fibers.

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Fabrication: The portion of the glass fiber production process where the forming cakes are put into creels and "roved" or fabricated onto doffs.

Fabricator: Manufacturer of reinforced plastic products.

Fall: The shape of the pattern of chopped fibers as they drop from the chopper to the bed.

Fan or Curtain: The chopped bundles which fall or are thrown off the chopper and cot.

Fatigue: The failure or decay of mechanical properties after repeated applications of stress. Fatigue tests give information on the ability of a material to resist the development of cracks, which eventually bring about failure as a result of a large number of cycles.

Fatigue Life: The number of cycles of deformation required to bring about failures of the test specimen under a given set of oscillating conditions (stresses and strains).

Fatigue Limit: The stress level below which a material can be stress cyclically for an infinite number of times without failure.

Fatigue Strength: The maximum cyclical stress a material can withstand for a given number of cycles before failure occurs. The residual strength after being subjected to fatigue.

Fiber: Reinforcement material which is a major component in a composite matrix. Often, fiber is used synonymously with filament.

Fiber Content: The amount of fiber present in a composite. This is usually expressed as a percentage volume fraction or weight fraction of the composite.

Fiber Diameter Letter Designation: Fibers are generally classified in hundred thousandths, i.e. a "K" fiber has a mean average diameter of 50+ to 55 height.

Letter Designation	Range of Fiber Diameter Up to and Including
A	.00006 in. (1.50 mi.)	.00010 in. (2.50 mi.)
B	.00010 in. (2.515 mi.)	.00015 in. (3.81 mi.)
C	.00015 in. (3.81 mi.)	.00020 in. (5.08 mi.)
D	.00020 in. (5.08 mi.)	.00025 in. (6.35 mi.)
E	.00025 in. (6.35 mi.)	.00030 in. (7.62 mi.)
F	.00030 in. (7.62 mi.)	.00035 in. (8.89 mi.)
G	.00035 in. (8.89 mi.)	.00040 in. (10.12 mi.)
H	.00040 in. (10.12 mi.)	.00045 in. (11.43 mi.)
J	.00045 in. (11.43 mi.)	.00050 in. (12.70 mi.)
K	.00050 in. (12.70 mi.)	.00055 in. (13.97 mi.)
L	.00055 in. (13.91 mi.)	.00060 in. (15.24 mi.)
M	.00060 in. (15.24 mi.)	.00065 in. (16.51 mi.)
N	.00065 in. (16.51 mi.)	.00070 in. (17.78 mi.)
P	.00070 in. (17.78 mi.)	.00075 in. (19.05 mi.)
Q	.00075 in. (19.05 mi.)	.00080 in. (20.32 mi.)
R	.00080 in. (20.32 mi.)	.00085 in. (21.59 mi.)
S	.00085 in. (21.59 mi.)	.00090 in. (22.86 mi.)
T	.00090 in. (22.86 mi.)	.00095 in. (24.13 mi.)
U	.00095 in. (24.13 mi.)	.00100 in. (25.40 mi.)
NOTE: The letters I and O are not used in this sequence.

Fiber Direction: The orientation or alignment of the longitudinal axis of the fiber with respect to a stated reference axis.

Fiber glass: Primarily means glass in fiber form. However, "fiber glass" is also used to describe composite processing and applications. Examples of usage: fiber glass molding plant, fiber glass car.

Fiberglass Reinforcement: Major material used to reinforce plastic. Available as mat, roving, fabric, and so forth, it is incorporated into both thermosets and thermoplastics.

Fiber Pattern: Visible fibers on the surface laminates or molding. The thread size and weave of glass cloth.

Fiber Reinforced Plastic (FRP): A general term for a composite that is reinforced with cloth, mat, strands, or any other fiber form.

Filament: A single, threadlike fiber of glass.

Filament Winding: Process, which involves winding a resin-saturated strand of glass filament around a rotating mandrel.

Filament Yarn: A yarn composed of continuous filaments assembled with or without twist.

Fill: The system of yarns running crosswise in a fabric (short for filling). Also known as weft. See Warp.

Filler: An inexpensive substance which is added to plastic resins to extend volume, improve properties, and lower cost.

Fines: Bundles that have been split apart into smaller bundles which are composed of only a few or single filaments. Fuzz is usually made of fines.

Finish: See Size.

Fire Retardants: Certain chemicals that are used to reduce the tendency of a resin to burn.

Fish Eye: Effect of surface contamination, which causes a circular separation of a paint or gel coat.

Flammability: This property describes how fast a plastic material will burn when subjected to a particular ASTM test. In this test, a flame is applied to one end of a strip of material. When the material starts burning the flame is removed and the time to consume a given amount of material is measured. Units - inches per minute (in/min.). Higher numbers indicate that the material will burn faster under conditions of this particular test. S.E. means self extinguishing. If a material is classified as S.E., the specimen stops burning when the flame is taken away.

Flash: That portion of the charge, which flows from or is extruded from the mold cavity during the molding. Extra plastic attached to a molding along the parting line, which must be removed before the part is considered finished.

Flash Point: Lowest temperature at which a substance gives off enough vapors to form a flammable mixture.

Flexible Molds: Molds made of rubber or elastomeric plastics, used for casting plastics. They can be stretched to remove cured pieces with undercuts.

Flexural Modulus: This is a number associated with the stiffness of materials. It is used to calculate how far a bar will bend when a bending load is applied to it. Units are normally millions of pounds per square inch. (106 psi) - Giga Pascals (gPa). Higher numbers for materials mean that they are more resistant to deflection when equal thickness are being compared.

Flexural Strength: This is also known as bending strength. It describes how much of a nonmoving load can be applied before a bar yields or breaks. Units are normally thousands of pounds per square inch. (103 psi) - Mega Pascals (mPa). Higher numbers mean that material is stronger and can withstand a heavier load.

Flow: The movement of resin under pressure, allowing it to fill all parts of a mold. The gradual but continuous distortion of a material under continued load, usually at high temperatures; also called creep.

Flow Line: A mark on a molded piece made by the meeting of two flow fronts during molding. Also called striae, weld mark, or weld line.

Flow Marks: Wavy surface appearance of an object molded from thermoplastic resins, cased by improper flow of the resin into the mold.

Fly: Fibers which fly out into the atmosphere during handling and processing.

Foam: Lightweight, cellular plastic material containing glass-filled voids. Typical foams include urethane, PVC, and polyester.

Force: The male half of the mold that enters the cavity, exerting pressure on the resin and causing it to flow. Also called punch.

Forming: The portion of the glass fiber production process where the fibers are drawn, attenuated from molten glass, and collected in forming cakes.

Forming Cakes or "Cakes": The package of glass fibers which is produced in forming. This package is generally on a tube and is placed on a forming carrier and sent through a drying/curing oven. These "cakes" are subsequently put into a roving creel and collected together into a roving doff.

Fracture: The separation of a body. Defined both as rupture of the surface without complete separation of laminate and as complete separation of a body because of external or internal forces.

Fracture Stress: The true, normal stress on the minimum cross-sectional area at the beginning of fracture.

Fracture Toughness: A measure of the damage tolerance of a material containing initial flaws or cracks. Used in aircraft structural design and analysis.

FRP: Acronym for fiber glass-reinforced or fiber-reinforced plastic, polymer or polyester.

Fuzz: Creel Fuzz - In glass fiber manufacturing, the broken filaments found around and on a roving creel. Chopper Fuzz - In Composite Fabrication, the broken filaments found around the glass cutter or chopper. See Fines. In the field, the broken filaments found around a roving pallet.

Fuzz Plug: Small, broken, compacted filaments of glass which collect inside the guide eye tubes which feed the chopper and cause the glass to stop running through it.

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Gate: Where the molten thermoplastic enters the cavity in the injection molding tool.

Gel: A partial cure of plastic resins; a semisolid, jelly-like state similar to gelatin in consistency.

Gel: The initial jelly-like solid phase that develops during the formation of a resin from a liquid. A semisolid system consisting of a network of solid aggregates in which liquid is held.

Gelation: The point in a resin cure when the resin viscosity has increased to a point such that it barely moves when probed with a sharp instrument.

Gel Coat: Surface coat of a specialized, quick-setting polyester resin, either colored or clear, providing a cosmetic enhancement and weather ability to a fiberglass laminate. The gel coat becomes an integral part of the finished laminate.

Gel Point: The stage at which a liquid begins to exhibit pseudo-elastic properties. This stage may be conveniently observed from the inflection point on a viscosity time plot.

Gel Time: Time required to change a flowable liquid resin into a non-flowing gel.

GFRP: Glass fiber-reinforced plastic, polymer or polyester.

Glass Blends: When several different fiber types, i.e. different lengths and diameters, are blended in the fiber slurry.

Glass Content: Percentage of glass in the compound.

Glass Fiber Wet-Process: Process of forming a glass mat on modified papermaking equipment.

Glass Transition: Reversible change in the amorphous polymer or in amorphous regions of a partially crystalline polymer from, or to, a viscous or rubbery condition to, or from, a hard and relatively brittle one.

Glass Transition Temperature (Tg): The appropriate midpoint of the temperature range over which glass transition takes place.

Good Side: Side of a molding in contact with a mold surface.

Graphite Fiber: A fiber made from a precursor by oxidation, carbonization, and graphitization process (which provides a graphitic structure).

Green: Resin, which has not completely cured and is still rather soft and rubbery.

Green Strength: That ability of the material, while not completely cured, to undergo removal from the mold and handling without tearing or permanent distortion.

GRP: Glass-reinforced plastic, polymer or polyester. This derivation is commonly used in Europe.

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Hand: The softness of a piece of fabric, as determined by the touch (individual judgment).

Hand Lay-up: The process of placing (and working) successive plies of reinforcing material or resin-impregnated reinforcement in position on a mold by hand. Method of molding room temperature curing thermosetting polymers, mainly epoxies and polyesters, in association with glass, mineral, or fiber reinforcements. Catalyzed resin mixtures are sprayed, brushed, or spatulated on a mold. A precut reinforcing layer is laid on the wet resin. After the resin soaks into the reinforcement, subsequent layers are built up to the required thickness and are cured, removed from the mold and trimmed. Some variations of hand lay-up techniques are bag molding, drape molding, vacuum molding and spray-up molding. Typical parts are custom auto bodies and boat hulls.

Hardener: A substance or mixture added to a plastic composition to promote or control the curing action by taking part in it.

Hard Glass: A roving product that is not very soluble in acetone or styrene which results in the tendency of the individual bundles to retain their integrity (hardness) and not filamentize in the matrix resin. Hard glass is often stiff and brashy. The size is generally less than 40% soluble in acetone. See Soft Glass.

Hardness: The resistance to surface indentation usually measured by the depth of penetration (or arbitrary units related to the depth of penetration) of a blunt point under a given load using a particular instrument according to a prescribed procedure.

Heat Cleaning: Batch and continuous processes in which organic yarn binder is removed from glass fabrics.

Heat Distortion Point: Temperature at which the strength of a material begins to degrade. Now called deflection temperature.

Heat Resistance: The property or ability of plastics and elastomers to resist the deteriorating effect of elevated temperatures.

Heat Sink: A contrivance for the absorption or transfer of heat away from a critical element or part. Bulk graphite is often used as a heat sink.

Heat Distortion Temperature: This is a measurement of the temperature which will cause the material to bend under a give load. It was developed for thermoplastic materials which soften considerably when heated. It has relatively little value as a design figure for thermosetting reinforced plastics. During this test a load is applied in bending to cause 264 psi stress in the material. The temperature of the material is then raised until the material bends one tenth of an inch at the center. Units - degrees Fahrenheit (°F)- degrees Centigrade (°C). Higher numbers mean that the material can be heated to a higher temperature before it deflects one tenth of an inch under this arbitrary load of 264 psi.

Helical Winding: In filament wound items, a winding in which a filament band advances along a helical path, not necessarily at a constant angle except in the case of a cylinder.

Het-Acid Resin: Polyester resin with exceptional fire qualities.

High-Pressure Laminates: Laminates molded and cured at pressures not lower than 6.9 MP (1.0 ksi), and more commonly in the range of 8.3 to 13.9 Mpa (1.2 to 2.0 ksi).

Homogeneous: Descriptive term for a material of uniform composition throughout.

Homopolymer: A compound produced by polymerization.

Honeycomb: Manufactured product of resin-impregnated sheet material (paper, glass, fabric, and so on) or metal foil, formed into hexagonal-shaped cells. Used as a core material in sandwich construction.

Hoop Stress: The circumferential stress in a material of cylindrical form subjected to internal or external pressure.

Hybrid: A composite laminate consisting of laminate of two or more composite material systems. A combination of two or more different fibers, such as carbon and glass or carbon and arimid, into a structure.

Hydraulic Press: A press in which the molding force is created by the pressure exerted by a fluid.

Hygroscopic: Material that absorbs moisture from the air.

Hysteresis: The energy absorbed in a complete cycle of loading and unloading. This energy in converted from mechanical to friction energy (heat).

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Ignition Loss: The difference in weight before and after burning. As with glass, the burning off of the binder or size.

Impact Strength-IZOD: A moving load is one that is moving when it strikes a bar. The effect of such a load which is denoted by the work "impact". The impact strength of a material is a measure of how much energy is absorbed by the bar when it is broken by a moving weight. There are many different test methods for measuring impact. Izod is but one of these methods. Units - foot pounds per inch of width. This is sometimes given as foot pounds per inch of notch. Joules/Meter (J/M). Higher numbers mean that the material will absorb more energy before it is broken by a moving weight.

Impact Test: Measure of the energy necessary to fracture a standard sample by an impulse load.

Impregnate: In reinforced plastics, to saturate a reinforcement, especially fiberglass, with a resin.

Inhibitor: A substance that retards polymerization, thus extending shelf life of a monomer. Also used to influence gel time and exotherm.

Initiator: Peroxides used as sources of free radicals. They are used in free-radical polymerization, for curing thermosetting resins, as cross-linking agents for elastomers and polyethylene, and for polymer modification.

Injection Molding: Method of forming a plastic to the desired shape by forcing the heat-softened thermoplastic polymer into a relatively cool cavity under pressure or thermosetting polymer into a heated mold.

Inorganic Pigments: Natural or synthetic metallic oxides, sulfides, and other salts that impart heat and light stability, weathering resistance, color, or migration resistance to plastics.

Insert: An integral part of plastic molding consisting of metal or other material that may be molded into the part or pressed into position after the molding is completed.

In-Situ: In place. In the position which it will finally occupy, e.g. molding or forming foam.

Interface: A surface that lies between two different materials.

Interlaminar: Descriptive term pertaining to an object (for example, voids), event (for example, fracture), or potential field (for example, shear stress) referenced as existing or occurring between two or more adjacent laminae.

Interlaminar Shear: Shearing force tending to produce a relative displacement between two laminae in a laminate along the plane of the interface.

Intumescent: Fire-retardant technology which causes an otherwise flammable material to foam, forming an insulating barrier when exposed to heat.

Irreversible: Not capable of re-dissolving or re-melting. Chemical reactions that proceed in a single direction and are not capable of reversal (as applied to thermosetting resins).

Isocyanate Plastics: Plastics based on resins made by the reaction or organic isocyanates with other compounds.

Isophthalic: Polyester resin based on isophthalic acid, generally higher in properties than a general purpose or orthothatic polyester resin.

Isotropic: Having uniform properties in all directions.

Izod Impact Test: A test for shock loading in which a notched specimen bar is held at one end and broken by striking, and the energy absorbed is measured.

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Jackstrawing: Visual effect of glass fiber turning white in a cured laminate. It may not effect the strength of a laminate, but could indicate air entrapment or water contamination.

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Kevlar: An organic polymer composed of aromatic polyamides having a para-type orientation (parallel chain extending bonds from each aromatic nucleus).

Knitted Fabric: A textile structure produced by interlooping one or more ends of yarn or comparable material.

Knot: The means of joining the strands of two doffs of roving. The knot is generally a reduced triple loop surgeon's knot, square knot or overhand knot.

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Laminat: Composite material system made with layers of fiber reinforcement in a resin. Sometimes used as a general reference for composites, regardless of how made.

Laminate: Primarily means a composite material system made with layers of fiber reinforcement in a resin. Sometimes used as a general reference for composites, regardless of how made. Examples of usage: laminate consumption by market, compression-molded laminate.

Laydown: A characteristic of the bed of chopped glass fibers which relates to the degree of uniformity in thickness that the bed exhibits across the width of the chopped pattern.

Layer: The horizontal plane of doffs on a pallet. A pallet usually has four layers of twelve doffs each. (Also see Cell).

Lay-up: Act of building up successive layers of polymer and reinforcement. Layers of catalyzed resin and fiberglass or other reinforcements are applied to a mold in order to make a part. The reinforcing material placed in position in the mold. The process of placing the reinforcing material in position in the mold. The resin-impregnated reinforcement.

Liquid-Crystal Polymer: A newer thermoplastic polymer that is melt process able and develops high orientation in molding, with resultant tensile strength and high-temperature capability.

Load-Deflection Curve: A curve in which the increasing tension, compression, of flexural load are plotted on the ordinate axis and the deflections caused by those loads are plotted on an abscissa axis.

Loom: A mechanical device that interlaces fibers at right angles with varying degrees of weave construction (weight, thickness and design). More modern looms are air jet but rapier and more traditional shuttle equipment is still in use.

Loom Beam: A large, flanged cylinder onto which all warp yarns are wound and from which yarns enter the loom.

Loop: Small open place in the strands due to the excessive length of one or more strands.

Loss on Ignition: Weight loss, usually expressed as percent of total, after burning off an organic sizing from glass fibers, or an organic resin from a glass fiber laminate.

Low-pressure Laminates: Laminated, molded, and cured using pressures from 400 psi down to and including the pressure obtained by mere contact of the plies.

Lubricant: A material added to most sizing to improve the handling and processing properties of textile strands.

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Mandrel: The core tool around which resin-impregnated paper, fabric, or fiber is wound to form pipes, tubes, or structural shell shapes.

Manipulator: Highly efficient system which eliminates the need for a press screw driven frame structure that opens and closes the mold in a controlled line of draw to prevent tool damage. See Megaject Pro.

Mat: A fibrous material for reinforced plastic consisting of randomly oriented chopped filaments, short fibers (with or without a carrier fabric), or swirled filaments loosely held together with a binder.

Matched Metal Molding: A reinforced plastics manufacturing process in which matching male and female metal molds are used (also called compression molding) to form the part, with time, pressure, and heat.

Matrix: The resin component of a polymer composite. Both thermoplastic and thermoset resins may be used, as well as metals, ceramics, and glasses. The plural is matrices.

Mat Strength: Ability of the mat to resist being pulled apart under tension during impregnation and molding.

Matchsticks: Strand-to-strand adhesion. A matchstick is a wide bundle that has 3 to 4 times as many filaments in it as do the majority of the bundles in the bed.

Matrix: Term used to describe the resin component of a polymer composite. An example of usage would be: "The glass fibers are reinforcing a polyester matrix." The plural is matrices.

Mechanical Properties: The properties of a material, such as compressive and tensile strengths, and modulus, that are associated with elastic and inelastic reaction when force is applied. The individual relationship between stress and strain.

Melamine: Thermoset resin.

Metallic Fiber: Manufactured fiber composed of metal, plastic-coated metal, metal-coated plastic, or core completely covered by metal.

Microballoons: Microscopic bubbles of glass, ceramic or Phenolic, used as a filler or to create syntactic foam or putty mixtures.

Microcracking: Crack formed in composites when thermal stresses locally exceed the strength of the matrix.

Mil: The unit used in measuring the diameter of glass fiber strands ( 1 mil = 0.001 in.).

Milled Fiber: Continuous glass strands hammer milled into very short glass fibers. Useful as inexpensive filler or anti-crazing reinforcing filler for adhesives.

M.I.T™: See Multiple Insert Tooling.

MPG: See Mold Protection Guard.

Modulus, Initial: The slope of the initial straight portion of a stress strain or load-elongation curve.

Modulus of Elasticity: Describes a material's ability to bend without losing its ability to return to its original physical properties.

Moisture: The amount of volatiles on the glass expressed as a percentage of the total weight.

Moisture Content: The amount of moisture in a material determined under prescribed conditions, and expressed as a percentage of the mass of the moist specimen, that is, the mass of the dry substance plus the moisture present.

Mold: The cavity or matrix into or on which the plastic composition is placed and from which it takes form. The tool used to fabricate the desired part shape.

Molded Edge: An edge that is not physically altered after molding for use in final form, and particularly on that does not have fiber ends along its length.

Molding: The forming of a polymer or composite into a solid mass of prescribed shape and size.

Molding Cycle: The period of time required for the complete sequence of operations on a molding press to produce one set of moldings.

Molding Pressure: The pressure applied to the ram of an injection machine or compression or transfer press to force the softened plastic to fill the mold cavities completely.

Mold Protection Guard: Mold protection guard. Prevents the over pressurization of the RTM mold during the injection process. See MPG.

Mold-Release Agent: A lubricant, liquid, or powder (often silicone oils and waxes), used to prevent sticking of molded articles in the cavity.

Multiple Insert Tooling: Low risk, high output composite tooling breakthrough. MIT tooling technology offers the composite molder quick-change multiple mold surfaces without multiple tooling costs. As each surface is an exact clone of its counterpart the replication of mold cavity accuracy, and therefore molded part, is guaranteed. See What is M.I.T?

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Non-Air-Inhibited Resin: Resin in which the surface cure will not be inhibited or stopped by the presence of air.

Non-Woven Fabric: A textile structure produced by bonding or interlocking of fibers, or both, accomplished by mechanical, chemical, thermal, or solvent means and combinations thereof.

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Orange Peel: Gel coated or painted finish, which is not smooth and is patterned similar to an orange's skin.

Organic: Matter originating in plant or animal life or composed of chemicals of hydrocarbon origin, either natural or synthetic.

Orientation: Position with relation to flow of polymer in mold.

Orthophthalic Resin: Polyester resin based on Orthophthalic acid, also known as a general purpose resin (GP).

Overlay Sheet: A non-woven fibrous mat (of glass, synthetic fiber, and so forth) used as the top layer in a cloth or mat lay-up, to provide a smoother finish, minimize the appearance of the fibrous pattern, or permit machining or grinding to a precise dimension. Also called surfacing mat.

Overspray: A specially formulated binder applied to texturized yarn that helps retain the bulk of the yarn after texturizing.

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PBT: Polybuthlene Therephthalate (Thermoplastic Polyester Resin).

PET: Polyethylene Terephthalate (Thermoplastic Polyester Resin).

Phenolic Resin: Thermosetting resin produced by the condensation of an aromatic alcohol with an aldehyde, particularly of phenol with formaldehyde. Used in high-temperature applications with various fillers and reinforcements.

Pigment: A colorant added to gel coat or resin.

Pinholes: Small holes on the exposed gel coated surface. They are about the diameter of common pins and may be easily counted.

Plastic: Material that contains as an essential ingredient an organic polymer of large molecular weight, hardeners, fillers, reinforcements, and so forth; is solid in its finished state, and, at some stage in its manufacture or its processing into finished articles, can be shaped by flow. Made of plastic. A plastic may be either thermoplastic or thermoset.

Plasticizers: Material incorporated in a plastic to increase its workability and flexibility. Normally used in thermoplastics. A lower molecular weight material added to an epoxy to reduce stiffness and brittleness, thereby resulting in a lower glass transition temperature for the polymer.

Plied Yarn: A yarn formed by twisting together two or more single yarns in one operation. (Synonyms: folded yarn, formed yarn.)

Plug: A composite industry name for a pattern or model.

Ply: The number of single yarns twisted together to form a plied yarn; also the number of plied yarns twisted together to form a cord. The individual yarn in a plied yarn or in a cord. One of several layers of fabric.

Poisson's Ratio: The ratio of transverse strain to axial strain during axial load.

Polyester Combination Yarn: A polyester/fiber glass hybrid yarn.

Polyester (Unsaturated): Product of an acid-glycol reaction commonly blended with a monomer to create a polymer resin. In its thermosetting form it is the most common resin used in the FRP industry.

Polymer: Chain molecule composed of many identical groups, commonly found in plastics.

Polymerization: Chemical bonding of polymer molecules during the curing reaction.

Porosity: Entrapped gas bubbles or voids in a gel coat film.

Post Bake: See Post Cure.

Post Cure: A heat cycle a roving doff goes through after fabrication. This is generally used to help "set" the ribbon on the outside of the doff to improve the doff's stability and resistance to package collapse.

PPO: Polyphenylene Oxide (Thermoplastic Resin).

PPS: Polyphenylene Sulfide (Thermoplastic Resin).

Prepreg: Either ready-to-mold material in sheet form or ready-to-wind material in roving form, which may be cloth, mat, unidirectional fiber, or paper impregnated with resin and stored for use. The resin is partially cured to a B-stage and supplied to the fabricator, who lays up the finished shape and completes the cure with heat and pressure. The two distinct types of prepreg available are (1) commercial prepregs, where the roving is coated with a hot melt or solvent system to produce a specific product to meet specific customer requirements, and, (2) wet prepreg, where the basic resin is installed without solvents or preservatives but has limited room-temperature shelf life.

Pressure Bag: A membrane which conforms to the inside of a laminate laid up on a mold. The membrane or bag is then inflated applying pressure which consolidates and densifies the laminate.

Print Through: Distortion in the surface of a part which allows the pattern of the core or fiberglass reinforcement to be visible through the surface. Also known as print out, telegraphing or read through.

Pultrusion: Continuous process for manufacturing composites that have a constant cross-sectional shape. The process consists of pulling a fiber-reinforcing material through a resin impregnation bath and through a shaping die, where the resin is subsequently cured.

Putty: Thickened mixture of resin made by adding fillers and reinforcing fibers.

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Reaction Injection Molding (RIM): Process for molding polyurethane, epoxy, and other liquid chemical systems. Mixing of two to four components in the proper chemical ratio is accomplished by a high-pressure impingement-type mixing head, from which the mixed material is delivered into the mold at low pressure, where it reacts (cures).

Re-Chop: Bundles which have clung to the chopper or cot which are chopped again into shorter lengths. Re-chop causes excessive chopper fuzz as the strands are cut and mashed into smaller bundles.

Reinforced Molding Compound: Compound consisting of a polymer and a reinforcement fiber or filler supplied by raw material producer in the form of ready-to-use materials.

Reinforced Plastics: Molded, formed, filament-wound, tape-wrapped, or shaped plastic parts consisting of resins to which reinforcing fibers, mats, fabrics, and so forth, have been added before the forming operation to provide some strength properties greatly superior to those of the base resin.

Reinforced Reaction Injection Molding (RRIM): A reaction injection molding with a reinforcement added. See Reaction Injection Molding.

Reinforcement: Strong material bonded into a matrix to improve its mechanical properties. Reinforcements are usually long fibers, chopped fibers, whiskers, particulates, and so forth. The term should not be used synonymously with filler.

Release Agent: Compound used to reduce surface tension or adhesion between a mold and a part.

Resin: Solid or pseudosolid organic material, usually of high molecular weight, that exhibits a tendency to flow when subjected to stress. Most resins are polymers. In reinforced plastics, the material used to bind together the reinforcement material. See Matrix and Polymer.

Resin-Rich Area: Localized area filled with resin and lacking reinforcing material.

Resin-Starved Area: Localized area of insufficient resin, usually identified by low gloss, dry spots, or fiber showing on the surface.

Resin Tearing: Separation of pigments in a gel coat affecting cosmetic appearance.

Resin Transfer Molding (RTM): A process whereby catalyzed resin is transferred or injected into an enclosed mold in which the fiberglass reinforcement has been placed. See RTM within the site.

Ribbon: The propensity of the glass bundles to "stick" together and act as a strand or end.

RIM: see Reaction Injection Molding.

Roving Doff or "Doff": The final product sold to the customer. It was made by roving or pulling together a group of forming cakes (the number of which depends upon the product being made).

Roving: A collection of untwisted strands wound together into a doff (ball). Also another name for the fabrication process step.

RP: Reinforced plastic, polymer or polyester.

RRIM: See Reinforced Reaction Injection Molding.

RTM: See Resin Transfer Molding. See also RTM within the site.

RTM Light: See Vacuum Molding. See also VM within the site.

RTP: Sometimes used to distinguish reinforced thermoplastic from reinforced thermosetting plastic.

Rule-of-Mixtures: When combined, the properties of the composite material is some combination of the properties of the two constituent materials. The composite property equals the amount of the fiber property multiplied by the volume percentage of fiber, plus the amount of matrix property multiplied by the volume percentage of matrix.

Run-Out: The process of pulling the glass from the doff to the chopper.

Runner: The channel through which thermoplastic material moves through a mold.

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SAN: Styrene Acrylonitrile (Thermoplastic Resin).

Sandwich Constructions: Panels composed of a lightweight core material, such as honeycomb or foamed plastic, to which two relatively thin, dense, high-strength or high-stiffness faces or skins are adhered.

S Glass: A family of magnesium-alumina-silicate glasses with a certified chemical composition which conforms to an applicable material specification and which produces high mechanical strength.

Scrim: A light, woven or non-woven fabric with relatively large openings between the yarns, used as reinforcement for paper and other products.