Polystyrene(PS) is a polymer of styreneis a polymer made from the monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry. At room temperature, polystyrene is normally a solid thermoplastic, but can be melted at higher temperature for molding or extrusion, then resolidified. High molecular weight thermoplastic resins produced generally by the free-radical polymerization of styrene monomer [C6H5CHCH2] which can be initiated by heating alone but more effectively by heating in the presence of free-radical initiator (such as benzoyl peroxide [(C6H5CO)2O2]. Typical processing techniques are modified mass polymerization or solution polymerization, suspension polymerization, and expandable beads.

The bright and clear polystyrene is usually found in food packaging such as clear drinking cups and disposable salad boxes because it is lightweight, tansparent, rigid and clean. When gaseous blowing agent is added into polystyrene, the solid plastic is expanded into a foam through the use of heat, usually steam. Extruded polystyrene (XPS), which is different from expanded polystyrene (EPS), is commonly known by the trade name Styrofoam. The voids filled with trapped air give it low thermal conductivity. This makes it ideal as a construction material and it is therefore sometimes used in structural insulated panel building systems.The common applications of high-impact polystyrene include use in computer side parts, TV case, home appliances and toys.