Polystyrene is a plastic with a wide range of uses, the most common being expanded polystyrene, a compact white foam used to pack and cushion fragile objects from knocks and vibrations and for thermal insulation in buildings. However, it is also found in office equipment, CD cases, models, fresh food trays and disposable dishware. Chemically, polystyrene is a polymer of the styrene CH2=CH-[phenyl].