There are two main types of polymer used for resins: thermosets and thermoplastics. The thermosetting polymers used in the construction industry are the polyesters and the epoxides. There are many thermoplastic resins used in composite manufacture: polyolefins, polyamides, vinylic polymers, polyacetals, polysulphones, polycarbonates, polyphenylenes and polyimides.
A wide range of amorphous and crystalline materials can be used as the fibre. In the construction industry the most common fibre used is glass fibre (there are 4 types of glass fibre: E-glass, AR-glass, A-glass and high strength glass). Carbon fibre, of which there are 3 types (Type I, II, III) can be used separately or in conjunction with the glass fibre as a hybrid to increase the stiffness of a structural member or the area within a structure, so that the stiffness exceeds the value possible using only glass fibre. Aramid fibres can be used instead of glass fibres to give increased stiffness to the composite.
There has been considerable recent interest in naturally derived fibres for a variety of composite applications. Fibres commonly used include: flax, hemp, and jute.
Bundles of filaments are called strands and these are usually combined to form thicker parallel bundles called rovings. Assembled rovings are used in processes involving chopping of the fibres during the production of a composite e.g. SMC, spray-up, continuous sheet manufacture. Rovings are also manufactured by a direct technique in which all the filaments needed in the final roving (up to 4800) are all drawn simultaneously from one bushing. These rovings are called direct rovings and are used in weaving, pultrusion and filament winding. Strands may also be twisted to form several types of yarn; rovings or yarns may be used either individually or in the form of a woven fabric.
For structural applications it is mandatory to achieve some degree of flame retardance. Fire retardants are usually incorporated in the resin itself or as an applied gel-coat. Fillers and pigments are also used in resins for a variety of purposes, the former principally to improve mechanical properties and the latter for appearance and protective action.