Polystyrene is a synthetic polymer made from styrene monomer, which is a liquid petrochemical. It is a thermoplastic polymer which softens when heated and can be converted via semi-finished products, such as films and sheets, into a wide range of final articles.
Polystyrene can be rigid or foamed. General purpose polystyrene is clear, hard and brittle. Polystyrene is naturally transparent, but can be coloured with colorants.