Styrene Acrylonitrile (SAN) - Styrene and acrylonitrile monomers can be copolymerized to form a random, amorphous copolymer that has improved weatherability, stress crack resistance, and barrier properties. The copolymer is called styrene acrylonitrile or SAN. The SAN copolymer generally contains 70 to 80% styrene and 20 to 30% acrylonitrile. This combination provides higher strength, rigidity, and chemical resistance than polystyrene, but it is not quite as clear as crystal polystyrene and its appearance tends to yellow more quickly.

Styrene acrylonitrile (SAN) copolymers have been available since the 1940s. Initially the price of styrene acrylonitrile materials was too high for it to be used in more than a few specialized applications.