PAs are a group of semi-cyrstalline engineering thermoplastics which are quite similar to each other. They are produced by polimersing linear structured aliphatic or, in some cases, aromatic acids and amines; aromatic types are denoted by letters such as "T" for terephthalic monomers or "I" for isophthalic monomers. Each individual type of nylon is labeled with one or two number(s), e.g. Nylon 6 or Nylon 6,6; these are the most common and therefore defining types of nylon. The number stands for the number of carbon atoms within the acid and amine monomers. Single numbers mean the monomer is an alpha amino-acid (or its lactam) and the amide links in the polymer are all "head-to-tail". Two numbers mean the monomers are a diamine or diacid and the amide links alternate between "head-to-tail" and "tail-to-head". In case of two numbers the first one refers to the diamine, the second one to the diacid. Nylon polymers typically are strong, though but notch-sensitive plastics featuring good resilience and barrier properties, high resistance to fatigue and abrasion but also low swelling resistance in water (up to 3% volume expansion; especially when using thin sheets of PA). Nylon plastics tend to be hydrolysed by acids but are stable to oils, greases, alkaline media and other solvents.
Mainly used for producing engineering components, power tool casings and rocker box covers. Because of their resilience and high abrasion resistance, PAs are often used as monofilaments for fibres, brushes, clothings, carpets and other industrial Anwendung (bearings, bolts, nuts, wheels, etc.).