Composites Terms

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A programmed gradual increase/ decrease in temperature and/or pressure to control cure or cooling of composite parts.

Rate tools

Tools designed to be used repeatedly in a production setting to fabricate many parts rather than a single prototype or small number of demonstration parts.

Reaction injection molding (RIM)

A process involving high-pressure mixing of two highly reactive resin components to promote fast cure; primarily used in the molding of parts with polyurethane matrices.


A substance used in a chemical reaction to produce other substances.


Scrap composites (thermoset or thermoplastic) collected in-plant or from post-consumer sources and reground into pellets or fine powder for reuse in molding new parts, either as a new base material or in combination with virgin materials.

Reinforced reaction injection molding (RRIM)

A closed molding process that mixes two highly reactive resin components for cure. Reinforcement, generally flake glass or milled fibers, is added to one of the resin components to add strength and reduce thermal expansion.

Reinforced reaction injection molding (RRIM)

Reaction injection molding process in which one of the two mixed components is reinforced, usually with flake glass or milled fibers, to stiffen the part and reduce thermal expansion (see previous entry).


The key element added to a matrix to provide the required properties (primarily strength). Reinforcement forms range from individual short fibers to complex braided, woven or stitched textile forms.

Release agent

An specially formulated material placed between the mold and uncured resin/fiber (usually sprayed or painted on the mold surface) to prevent permanent bonding between the two during cure and facilitates demolding after cure.

Release film

A release agent made from an impermeable film that does not form a bond with the composite material during cure.


A solid or pseudo-solid polymeric material, often of high molecular weight, which exhibits a tendency to flow when subjected to stress, usually has a softening or melting range, and usually fractures conchoidally. As composite matrices, resins bind together reinforcement fibers and work with them to produce specified performance properties.

Resin content

See matrix content.

Resin transfer molding (RTM)

A closed molding process in which catalyzed resin is transferred into an enclosed mold cavity to impregnate a pre-positioned fibrous reinforcement (see preform). The mold and/or resin may or may not be heated. RTM involves relatively low tooling and equipment costs and enables fabricators to consolidate large parts.

Resin viscosity

Describes a resin system's solid-to-liquid transition resistance to flow, which can be altered by temperature and pressure to achieve desired flow characteristics. (Also see viscosity.)


Describes a localized buildup of resin in excess of the expected resin/fiber ratio in a composite.


Describes an area in a composite that lacks sufficient resin to achieve thorough fiber wetout.

Ribbon direction

On a honeycomb core, the length of the core splice; the direction perpendicular to the direction of cell expansion (w-direction). The direction of one continuous ribbon. (See honeycomb.)


Large filament-count tow; a collection of continuous glass fiber filaments, either as untwisted strands or twisted yarn.


See resin transfer molding.

RTM Light

A variant of resin transfer molding (RTM) in which vacuum pressure is used to hold two mold halves together while resin is injected at very low pressure (1 psi to 2 psi). The low pressure permits the use of lightweight, low-cost tooling.