Polystyrene, sometimes abbreviated as “PS”, is an aromatic polymer made from the chemical styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry. Polystyrene is a thermoplastic substance that normally exists in solid state at room temperature, but melts if heated (for molding or extrusion), and becomes solid again when cooled. Polystyrene can be recycled, and has the number “6” as its recycling symbol.

Polystyrene is one of the most widely used kinds of plastic. Pure solid polystyrene is a colorless, hard plastic with limited flexibility. It can be cast into molds with fine detail. Polystyrene can be transparent or can be made to take on various 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 drinks cups. Discarded polystyrene, which does not biodegrade, is often abundant in the outdoor environment, particularly along shores and waterways.