Synthetic fibers made from acrylonitrile copolymers with a content of acrylonitrile or polyacrylonitrile exceeding 85% (by weight percentage). Common monomers include non-ionic monomers such as methyl acrylate, methyl methacrylate, etc., with the third monomer being an ionic monomer, such as sodium acrylate.

Polyacrylonitrile fibers have properties very similar to wool, offering good elasticity; they can retain a rebound rate of 65% after stretching 20%. They are fluffy, curly, and soft, with better thermal insulation than wool by 15%, earning the nickname "synthetic wool." Their strength ranges from 22.1 to 48.5 cN/tex, up to 1 to 2.5 times higher than wool. They have excellent sunfastness, with a strength decrease of only 20% after one year of outdoor exposure, and can be used for curtains, drapes, tents, and protective clothing. They are resistant to acids, oxidizing agents, and most organic solvents, but have poor resistance to alkalis. The softening temperature of the fibers is between 190°C and 230°C.