Polyacrylonitrile (PAN) is a resinous, fibrous, or rubbery organic polymer. Almost all polyacrylonitrile resins are copolymers made from mixtures of monomers; with acrylonitrile as the main component. PAN fibers are the chemical precursor of high-quality carbon fiber. It is chemically modified to make the carbon fibers found in tennis rackets & high-tech bicycles.
Homopolymers of polyacrylonitrile have been used as fibers in hot gas filtration systems, outdoor awnings, sails for yachts, and even fiber reinforced concrete. Mostly copolymers containing polyacrylonitrile are used as fibers to make knitted clothing, like socks and sweaters, as well as outdoor products like tents and such. If the label of some piece of clothing says "acrylic", then it's made out of some copolymer of polyacrylonitrile.