Polystyrene (PS) is one of the generally widely used plastics, the scale being several billion kilograms per year.
Polystyrene can either be a thermoset or a thermoplastic. A thermoplastic polystyrene is in a solid (glassy) state at room temperature, but flows if heated above its glass transition temperature of about 100ºC, and becomes solid again when cooled. Absolute solid polystyrene is a colorless, hard plastic with partial flexibility. It can be transmit into molds with excellent detail. Polystyrene can be transparent or can be made to take on a variety of colors.
Solid polystyrene is used, for example, in disposable cutlery, plastic models, CD and DVD cases, and smoke detector housings. Products made from foamed polystyrene are nearly ubiquitous, for example packing materials, insulation, and foam drink cups.