Prepreg

A thermosetting resin based on molecules containing epoxide groups, cured by reaction with a hardener such as an amine or anhydride. Valued for strong adhesion, low cure shrinkage, chemical resistance and high mechanical performance, it is widely used in structural adhesives, laminating resins, coatings and composite matrices.

The process of placing reinforcement plies into or onto a mould in the specified sequence and orientation, by hand or by machine; also used as a noun for the resulting stack or its design. Hand layup with wet resin remains the basic process for GRP boat building and GRP roofing.

Intermediate vacuum compaction of a partially completed prepreg stack, carried out periodically during lay-up to remove trapped air and seat the plies before further layers are added. Regular debulks reduce wrinkling, bridging and final void content, especially on curved tooling.

Reinforcement in which virtually all fibres run in a single direction, supplied as dry tape, lightly stitched or bound fabric, or prepreg. Unidirectional plies give the highest stiffness and strength along the fibre direction but need supporting plies in other orientations.