We reference a wide range of materials and related technologies throughout our site. The below glossary offers a guide.


  • Advanced Composites – Composite materials applicable to aerospace construction and other high end applications, and made by imbedding high-strength, high-modulus fibers within an essentially homogeneous matrix.Synonyms: High performance composites
  • Amorphous Polymer – A polymer or plastic of which the molecular chains are arranged randomly with no long term order.
  • Anisotropic Material – A material which has different properties in different directions. A unidirectional fiber composite, for instance, is much stronger and stiffer along the fibers (in the longitudinal direction) than across them (in the transverse direction).
  • Annealing – In plastics, heating to a temperature at which the molecules have significant mobility, permitting them to reorient to a configuration having less residual stress.
  • Aramid – A type of highly oriented polymer used as reinforcing fibers in composites. The best known aramid fiber is Kevlar by DuPont.
  • Autoclave – A closed vessel capable of being heated under pressure using an inert gas (CO2 or N3) to transfer the heat and pressure to a laminate component in order to consolidate and cure.
  • Autoclave Molding – The process by which a layup in a mold or tool is cured or consolidated in an autoclave, rather than by some other means.
  • Axial Winding – In fiber placement, a winding with the filaments parallel to the long axis of the mandrel. The fiber tows are said to be at a 0˚ helix angle.


  • B-Stage – An intermediate stage in the reaction of a resin; that is, partial cure. In most thermoset prepregs, the resin has been cured to the b-stage.
  • Bagging – Applying an impermeable layer of film over an uncured part and sealing the edges so that a vacuum can be drawn.
  • Balanced Laminate – A composite laminate in which all laminate at angles other than 0˚ and 90˚ occur only in +/- pairs (not necessarily adjacent) and are symmetrical around the centerline.
  • Bearing Strength – The 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 – If the edges of two composite laminates are joined using a fastener, and then tension is applied, the bearing stress is the stress of the fastener.
  • Bidirectional Laminate – A reinforced plastic laminate in which the fibers are oriented in more than one direction in the plane of the laminate.
  • Bismaleimide – A type of thermoset that cures by an addition reaction, avoiding formation of volatiles, and has temperature capabilities between those of epoxy polyimide.
  • Bleeder Cloth – Material, such as fiberglass, 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.
  • Bond – The adhesion of one surface to another, with or without the use of an adhesive as a bonding agent.
  • Bond Strength – As measured by load/bond area, the stress required to separate a layer of material from that to which it is bonded.
  • Boron Fiber – A fiber usually of the tungsten-filament core with boron vapor deposited on it to impart strength and stiffness. Boron fibers are heavier than carbon or graphite fibers and are more expensive.
  • Butt Joint – A joint in which parts are jointed with no overlap.


  • C-Scan – A non-destructive inspection method of detecting delaminations and voids in composite laminates using ultrasonics. The part must be placed in a tank of water and scanned in transmission to produce a picture of the damage. C-scan results are easier to interpret than a-scan signals, but c-scan is usually limited to flat or mildly curved parts which will fit into the tank.
  • Carbon – A more ordered form of carbon. Diamond is the densest crystalline form of carbon.
  • Carbon-Carbon – A composite material consisting of carbon or graphite fibers in a carbon or graphite matrix.
  • Ceramic – A rigid, frequently brittle material made from clay and other inorganic, nonmetallic substances and fabricated into articles by sintering, that is, cold molding followed by fusion of the part at high temperature.
  • Circumferential Winding – A type of fiber placement in which the filaments are perpendicular to the axis.
  • Co-consolidation – A processing step where two or more thermoplastic preformed parts are joined by being placed against each other in a fixture or tool and heated under pressure to melt the matrix resin.
  • Co-curing – The act of curing a composite laminate and simultaneously bonding it to some other prepared surface (such as stiffeners), or curing together an inner and outer tube of similar or dissimilar fiber-resin combination after each has been wound or wrapped separately.
  • Coefficient of Thermal Expansion – A material’s fractional change in length or volume for a given unit change of temperature.
  • Cohesion – The propensity of single substance to adhere itself. The internal attraction of molecular particles toward each other. The ability to resist partition of itself. The force holding a single substance together.
  • Compaction – The application of a temporary vacuum bag and vacuum to remove trapped air and compact to layup.
  • Composite – A material created from a fiber (or reinforcement) and an appropriate matrix material in order to maximize specific performance properties. The constituents do not dissolve or merge completely but retain their identities as they act in concert. The matrix acts as a load transfer medium between fibers.
  • Composite Material – A combination of two or more materials (reinforcing elements, fillers, and composite matrix binder), differing in form or composition on a macroscale. 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 and interface between one another.
  • Computer Aided Design (CAD) – The use of a computer to develop the design of a product to be manufactured. The use of a computer to develop the design and necessary NC programs for use by the manufacturing equipment which will produce a product.
  • Consolidation – A process that fuses each ply together by tacking and flowing the matrix between plies. Usually involves heat and pressure.
  • Continuous Filament – An individual, small-diameter reinforcement that is flexible and indefinite in length.
  • Creep – The irreversible dimensional change in a material under mechanical load overtime.
  • Crystallinity – In polymers, a microstructure in which the linear molecular chains are arranged in an orderly fashion. Branched or network polymers are not crystalline. Even linear polymers are not entirely crystalline, but have pockets of order within their bulk. They are, therefore, said to be “semi-crystalline.
  • Cure – To change the physical properties of a thermoset resin irreversibly by chemical reaction via heat and catalysts, alone or in combination, with or without pressure.
  • Cure Cycle – The time/temperature/ pressure cycle used to cure a thermosetting resin system or prepreg.


  • Delamination – The separation of a laminated plastic material between plies.


  • E-Glass – “Electrical glass
  • Epoxy Plastic – 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.


  • Fatigue Life – The number of cycles of deformation required to bring about failure of the test specimen under a given set of oscillating conditions (stresses or strains).
  • Fiber – A single homogeneous strand of material, essentially one-dimensional, used as a principal constituent in composites because of its high axial strength and modulus.
  • Fiber Orientation – The fiber alignment in a non-woven or a mat laminate in which most of the fibers are the same direction, thereby affording higher strength in that direction.
  • Fiber Placement (FP) – Automated Fiber Placement (AFP) is traditionally differentiated from Tape Laying by considering the process to utilize a plethora of narrow, individual slit tapes or tows to make up a given total prepreg band width. Complex geometries that demand complex fiber placement are typically approached by the industry with multiple 0.125 inch – 0.250 inch tows. While this solution usually conquers the geometry challenge, it adds to machine complexity and cost and increases manufacturing time. A compromise approach, geometry dependent, may be to utilize multiple 0.500 inch tapes to improve throughput, while still maintaining good laminate quality on the complex surface.
  • Fiberglass – An individual filament made by drawing molten glass. A continuous filament is a glass fiber of great or indefinite length. A staple fiber is a glass fiber of relatively short length, generally less than 430mm (17 in.), the length related to the forming or spinning process used.


  • Graphite – The crystalline allotropic form of carbon.
  • Graphite Fiber – A fiber made from a precursor by oxidation, carbonization, and graphitization process.


  • Hand Layup – The process of placing and working successive plies of reinforcing material or resin-impregnated reinforcement in position on a mold by hand.


  • Impact Strength – A material’s ability to withstand shock loading as measured by the energy absorbed in an impact test.
  • Impregnate – In reinforced plastics, to saturate the reinforcement with a resin.
  • Interlaminar Shear – Shearing force tending to produce a relative displacement between two lamina in a lamina along the plane of their interface.
  • Intralaminar – Descriptive term pertaining to an object (voids, etc.), event (fracture, etc.), or potential field (temperature gradient, etc) existing entirely within a single lamina without reference to any adjacent laminate.


  • Kevlar – DuPont’s trade name for aramid fibers. See also aramid.


  • Microcracks – Small cracks formed in composites when thermal stresses locally exceed the strength of the matrix. Since most microcracks do not penetrate the reinforcing fibers, microcracks in a cross-plied tape laminate or in a laminate made from cloth prepreg are usually, but not always, limited to the thickness of a single ply.
  • Modulus of Elasticity – The ratio of the stress or load applied to the strain or deformation produced in a material that is elastically deformed. Also called Young’s modulus.


  • Phenolic (phenolic resin) – A 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.
  • Ply – A single layer of a composite laminate. 2. A sheet of prepreg ready for inclusion in a laminate.
  • Polyamide – A thermoplastic polymer in which the structural units are linked by amide or thio-amide groupings (repeated nitrogen and hydrogen groupings). Many polyamides are fiber forming.
  • Polyamideimide – A polymer containing both amide (nylon) and imide (as in polyimide) groups; properties combine the benefits and disadvantages of both.
  • Polyether Etherketone (PEEK) – A linear semi-crystalline thermoplastic. A composite with a PEEK matrix may have a continuous-use temperature as high as 250˚C (480˚F).
  • Polyetherimide (PEI) – An amorphous polymer with good thermal properties for a thermoplastic. Reported Tg of 215˚C (419˚F) and continuous-use temperature of about 170˚C (338˚F).
  • Polyimide (PI) – A polymer produced by reacting an aromatic dianhydride with an aromatic diamine. It is a highly heat-resistant resin, > 315˚C (600˚F). Similar to a polyamide, differing only in the number of hydrogen molecules contained in the groupings. Suitable for use as a binder or adhesive. May be either thermoplastic or thermoset.
  • Polymer – A substance in which each molecule contains a large number of atoms bonded to each other in a long chain or a three-dimensional network of short chains bonded to each other. The main chain may be branched, that is, may have short chains attached along its length.
  • Polyphenylene Sulfide (PPS) – A high-temperature thermoplastic useful primarily as a molding compound. Optimum properties depend on slightly cross-linking the resin. Known for chemical resistance.
  • Polypropylene – A touch, lightweight, thermoplastic made by the polymerization of high-purity propylene gas in the presence of an organometallic catalyst at relatively low pressures and temperatures.
  • Polysulfone (PS) – A high temperature resistant thermoplastic polymer with the sulfone linkage, with a Tg of 190˚C (375˚F).
  • Polyurethane (PU) – A thermosetting resin prepared by the reaction of diisocyanates with polyols, polyamides, alkyd polymers, and polyether polymers.
  • Preimpregnation – The practice of mixing resin and reinforcement and effecting partial cure before use or shipment to the user. See also prepreg.
  • Prepreg – A combination of mat, fabric, nonwoven material, or roving impregnated with resin or other matrix material.


  • Reinforced Plastics – Molded, formed, filament-wound, tape-wrapped, or shaped plastic parts consisting of resins to which reinforcing fibers, mats, fabrics, etc., have been added before the forming operation to provide some strength properties greatly superior to those of the base resin.
  • Residual Stress – The stress existing in a body at rest, in equilibrium, at uniform temperature, and not subjected to external forces. Often caused by the forming and curing process.
  • Resin – A solid or pseudo-solid organic material, usually of high molecular weight, that exhibits a tendency to flow when subjected to stress. It usually has a softening or melting range, and fractures conchoidally. Most resins are polymers. In reinforced plastics, the material used to bind together the reinforcement material; the matrix.
  • Resin Content – The amount of resin in a laminate expressed as either a percentage total weight or total volume.


  • S-Glass – Structural glass; used as fiber reinforcement, designed to provide very high tensile strength.
  • Sandwich Constructions – Panels composed of lightweight core material, such as honeycomb or foamed plastic, to which two relatively thin, composite faces or skins are adhered. A sandwich construction is stronger in bending than the composite skins by themselves.
  • Semicrystalline – In plastics, exhibiting localized crystallinity. See also crystallinity.
  • Shear Strength – The maximum shear stress that a material is capable of sustaining before failure. Shear strength is calculated from the maximum load during a shear or torsion test and is based on the original cross-sectional area of the specimen.


  • Tape – Unidirectional prepreg fabricated in widths up to 305 mm (12in.) for carbon and 75 mm (3in.) for boron. Woven broad goods carbon and glass tapes up to 1250 to 1500 mm (50 or 60in.) wide are available commercially.
  • Tape Laying – A fabrication process in which prepreg tape is laid side by side or overlapped to form a structure.
  • Thermoplastic – A plastic material that is capable of being repeatedly softened by application of heat and repeatedly hardened by cooling. Softening and hardening are reversible for a thermoplastic.
  • Thermoset – A plastic material that is capable of being cured by heat or catalyst into an infusible and insoluble material. Once cured, a thermoset cannot be returned to the uncured state. Thus, hardening is irreversible for a thermoset.
  • Tow – An untwisted bundle of continuous filaments. Commonly used in referring to man-made fibers, particularly carbon and graphite, but also glass and aramid. A tow designated as 140K has 140,000 filaments.


  • Vacuum Bag Molding – A process in which a sheet of flexible transparent material plus bleeder cloth and release film are placed under the layup on the mold and sealed at the edges. A vacuum is applied between the sheet and the layup. The entrapped air is mechanically worked out of the layup and removed by the vacuum, and the part is cured with temperature, pressure, and time.
  • Vinyl Esters – A class of thermosetting resins containing esters of acrylic and/or methacrylic acids, many of which have been made from epoxy resin. Cure is accomplished as with unsaturated polyesters by copolymerization with other vinyl monomers, such as styrene.


  • Wet Layup – A method of making a reinforced product by applying the resin system as a liquid when the reinforcement is put in place. In prepreg layup, the resin and fiber are already together.
  • Wet-out – The condition of an impregnated roving or yarn in which substantially all voids between the sized strands and filaments are filled with resin.