Styrofoam is a close-celled extruded polystyrene that is made from a petroleum-based product known as styrene. It is refined into polystyrene through polymerization and a hydrofluorocarbon agent is added after polymerization. This combination lets it extrude and expand until the foam board is formed. It is made of 98% air that makes it buoyant, and lightweight. It is often misidentified as another material used for craft, which is expanded polystyrene and is green and white in colour. Styrofoam itself, however, is made by the Dow company and is blue in colour and used as an insulation building material and also in foundations of certain structures.