Polyoxymethylene is a type of plastic. It is made from a chain of alternating oxygen atoms and methylene bridges. It is also called polyformaldehyde, polyacetal, or simply acetal. Small polyoxymethylene molecules are called paraformaldehyde.
Polyoxymethylene is formally the name for the homopolymer of formaldehyde. Copolymers of formaldehyde are also sold as polyacetal or acetal, and have similar properties to the homopolymer.