The polyacrylonitrile resins are hard, relatively insoluble, and high-melting materials. Polyacrylonitrile (poly(vinyl cyanide)) is used almost entirely in copolymers. The copolymers fall into three groups: fibers, plastics, and rubbers. The presence of acrylonitrile in a polymeric composition tends to increase its resistance to temperature, chemicals, impact, and flexing.