Monofilament Yarn is a single plastic solid thread with cross section that is typically circular, flat or triangular. It may be made of two different polymers side-by-side or from a single polymer. Monofilament yarn is wound on individual spools and is available in various spool types.

This type of yarn is produced through the extrusion process, which involves passing a polymer through holes in spinnerets. The process is very similar to that used for fibrillated yarn, but tools and procedures are different. The first step in producing monofilament yarn is to find a polymer to use.

A standard PET monofilament yarn is produced by a two-step process. Its target diameter is 0.55 millimeters. Then, the yarn is tested for tensile strength using an ASTM D2256-97 procedure. It is also tested for abrasion resistance using a squirrel cage method.