Polyphthalamide (aka. PPA, High Performance Polyamide) is a thermoplastic synthetic resin of the polyamide (nylon) family that is used to replace metals in high temperature automotive applications, as the housing for high temperature electrical connectors and multiple other uses. It has found a degree of favor for use in cutlery. Cold Steel has advertised the glass fibre reinforced series as being stealthy (due to them not being detected by metal detectors and having no metallic reflections) and, being made of "Grivory" (a trade name), stronger than previous models made of "Zytel".
As a member of the nylon family, it is a semi-crystalline material composed from a diacid and a diamine. However, the diacid portion contains at least 55% terephthalic acid (TPA) or isophthalic acid (IPA). TPA or IPA are aromatic components which serve to raise the melting point, glass transition temperature and generally improve chemical resistance vs. standard aliphatic nylon polymers.
PPA is manufactured under trade names Amodel, Grivory, VESTAMID HTplus and Zytel(r) HTN.