Aromatic polyamides (polyparaphenylene terephthalamide) as reinforcing fibres are characterised by very high tensile strength and modulus, low density and good heat resistance. In composite form they outperform glass fibres on these properties when compared on an equal volume-fraction-of-reinforcement basis. Compressive strength, however, is much lower for aramid reinforced composites. Machining (sawing, drilling, grinding) of aramid reinforced composites required special tools and adjustment of machining conditions. Since aramid fibres absorb moisture, they should be dried prior to processing with resins.
Trade names for aramid fibres include “Kevlar”, grades 29, 49 and now 149. Kevlar 49 is the standard fibre grade for use in composites.
These fabrics are available as woven fabrics, ie. Plain weave, 2×2 Twill weave, 4 & 8 Harness satin weave; as well as stitched fabrics, ie. Biaxial ± 45°, triaxial 0/90 with ± 45°, quadraxial 0+90 with ± 45°.