Styrofoam™ Brand Square Edge XPS Extruded Polystyrene Insulation is a foam insulation board that meets the needs of the commercial foundation and building floor slab market. It also can be used for attics, foundations/slabs and crawlspaces in residential applications. The product’s closed-cell structure resists water pickup, enabling it to retain a high R-value over time – a necessary property in wet, below-grade commercial foundation applications.