- The "sandwich" polystyrene insulated panels have two layers of steel sheet between which lies a layer of density polystyrene and different thickness. They are used for the exterior and interior walls, and roofs and ceilings of the flats, buildings industrial, commercial, agricultural farms, buildings of offices, warehouses, areas of production and other special constructions. The inner layer polystyrene is known for suppression of thermal bridges and reduced weight, which does not affect the structure of resistance of the construction.