Pre-preg

Pre-preg is a term for "pre-impregnated" composite fibres where a material, such as epoxy is already present. These usually take the form of a weave or are uni-directional. They already contain an amount of the matrix material used to bond them together and to other components during manufacture. The resin is only partially cured to allow easy handling, this is call B-Stage material and requires cold storage to prevent complete curing. B-Stage pre-preg is always stored in cooled areas since complete polymerization is most commonly done by heat. Hence, composite structures built of pre-pregs will mostly require an oven or autoclave to finish the complete polymerization.

There are several advantages and disadvantages of the B-Stage pre-preg process in comparison to the hot injection process. Pre-preg allows one to impregnate the fibers on a flat workable surface, or rather in an industrial process, and then later form the impregnated fibers to a shape which could prove to be problematic for the hot injection process. Prepreg also allows one to impregnate a bulk amount of fiber and then store it in a cooled area for an extended period of time to cure later. Unfortunately the process can also be time consuming in comparison to the hot injection process.