Expanded Polystyrene

Expanded polystyrene, abbreviated EPS, is a rigid, lightweight foam insulation material made by expanding small beads of polystyrene plastic with steam until they fuse together into a block of mostly trapped air, distinct from extruded polystyrene in being formed from fused beads rather than a continuously extruded sheet, which gives EPS a slightly more open, granular structure and typically a lower cost. Developed commercially in the 1950s, it is widely used as rigid board insulation in walls, roofs and foundations, as the core of structural insulated panels, and as protective packaging, valued for its low cost, light weight and respectable insulating value, though it is more vulnerable to moisture absorption and physical crushing than denser foam insulation products.