Fabrics and fibers are pre-impregnated by the materials manufacturer, under heat and
pressure or with solvent, with a pre-catalyzed resin. The catalyst is largely latent at ambient
temperatures giving the materials several weeks, or sometimes months, of useful life when
defrosted. However to prolong storage life the materials are stored frozen. The resin is
usually a near-solid at ambient temperatures, and so the pre-impregnated materials (prepress)
have a light sticky feel to them, such as that of adhesive tape. Unidirectional materials take
fiber direct from a creel, and are held together by the resin alone. The prepress are laid up by
hand or machine onto a mould surface, vacuum bagged and then heated to typically 120-
180°C. This allows the resin to initially reflow and eventually to cure. Additional pressure
for the molding is usually provided by an autoclave (effectively a pressurized oven) which
can apply up to 5 atmospheres to the laminate.
Materials Options:
Resins: Generally epoxy, polyester, pheno