Polyoxymethylene (POM), also known as acetal resin, polytrioxane, polyformaldehyde, and paraformaldehyde, is an engineering plastic used to make gears, bushings and other mechanical parts (cf. nylon, teflon, UHMWPE). The most important polyacetal resin, it is a thermoplastic with good physical and processing properties. It is also sold under the trade names Delrin, Kepital, Celcon, "Hostaform" and Ultraform, the last three being copolymers.