Expanded Polystyrene (EPS)
Expanded polystyrene is a rigid and tough, closed-cell foam. It is usually white and made of pre-expanded polystyrene beads. Sheets are commonly packaged as rigid panels, which are also known as “bead-board”. Thermal resistivity is usually about 28 m·K/W (or R-4 per inch). Some EPS boards have a flame spread of less than 25 and a smoke-developed index of less than 450, which means they can be used without a fire barrier (but require a 15 minute thermal barrier) according to US building codes. A growing use of EPS in construction is insulating concrete forms. The density range is about 16–640 kg/m3. Expanded polystyrene is often used to insulate the interior of masonry basement walls. The rigid cellular structure provides thermal and acoustical insulation, strength with low weight, and coverage with few heat loss paths.