Extruded polystyrene is a type of insulation material with fine, closed cells, containing a mixture of air and refrigerant gas. Popularly known by its Dow trademark Styrofoam, it has a high R-value, good moisture resistance, and high structural strength compared to other rigid insulation materials. Both extruded polystyrene and the other common type of polystyrene foam, expanded polystyrene (EPS), are used extensively as thermal insulation in industrial, commercial, and residential construction. Most food service applications including meat trays, egg cartons, hamburger clam shells, foam plates, and trays are extruded polystyrene, although disposable coffee cups are made of expanded polystyrene.
Environmentally-damaging chlorofluorocarbons (CFCs) are used in the manufacture of extruded polystyrene, however the expansion agent for EPS material is pentane.