Expanded Polystyrene :

Expanded polystyrene is inflexible and hard, closed-cell foam. It is typically white and produces of pre-expanded polystyrene beads. Extended polystyrene can be used for disposable trays, plates, bowls and cups; and for carry-out food packaging (including the hinged lid containers popularly known as "clam shells"). Other uses contain molded sheets for construction insulation and packing material peanuts for cushioning fragile items inside boxes. Sheets are commonly packaged as rigid panels (size 4 by 8 or 2 by 8 feet) which are also recognized as bead-board.

Due to its mechanical properties such as low weight, rigidity, and formability, EPS can be used in a wide variety of different applications. Its market value is likely to increase to more than US$15 billion until 2020.

Thermal conductivity is measured according to EN 12667. Typical values range from 0.032 to 0.038 W/(m•K) subject on the density of the EPS board. The value of 0.038 W/(m•K) was obtained at 15 kg/m3 while the value of 0.032 W/(m•K) was obtained at 40 kg/m3 according to the data sheet of K-710 from StyroChem Finland. Adding fillers (graphites, aluminium, or carbons) has lately permitted the thermal conductivity of EPS to reach around 0.030–0.034 (as low as 0.029) and as such has a grey/black color which distinguishes it from standard EPS. Several EPS producers have produced a variety of these increased thermal resistance EPS usage for this product in the UK & EU.

Water vapor diffusion resistance (μ) of EPS is around 30–70.

ICC-ES (International Code Council Evaluation Service) needs EPS boards used in building construction meet ASTM C578 requirements. One of these necessities is that the oxygen index of EPS as measured by ASTM D2863 be greater than 24 volume %. Typical EPS has an oxygen index of around 18 volume %; thus, a flame retardant such as HBCD (hexabromocyclododecane), is added to styrene or polystyrene during the formation of EPS.

The boards containing HBCD when testing in a channel using test method UL 723 or ASTM E84 will have a flame spread index of less than 25 and a smoke-developed index of less than 450. ICC-ES needs the use of a 15-minute thermal barrier when EPS boards are used inside of a building.

According to EPS-IA ICF association, the usual density of EPS used for insulated concrete forms is 1.35 to 1.80 pcf. This is either Type II or Type IX EPS according to ASTM C578. EPS blocks or boards used in building construction are normally cut using hot wires.