Expanded polystyrene (EPS) is a rigid and tough, closed-cell foam with a normal density range of 11 to 32 kg/m³. It is usually white and made of pre-expanded polystyrene beads. A material widely known as styrofoam made by foaming the polystyrene(PS), a thermoplastic resin. As it is a foamed polystyrene, it is comprised of a large amount of air layers. 

Due to this characteristic, it has thermal insulation, impact absorption, water repellency, and sound insulation properties. It is thus widely used in multiple areas including protective packaging for home appliances, building insulators, food containers, and more.