Styrofoam™ Brand Square Edge Insulation is an extruded polystyrene foam (XPS) insulation board that meets the needs of the commercial foundation and building floor slab market and can also be used for attics, foundations/slabs and crawl spaces in residential applications. With more than 60 years of proven performance in wet environments, the closed-cell structure of Styrofoam™ Brand Square Edge Extruded Polystyrene Foam Insulation resists water pickup, enabling it to retain a high R-value over time - a necessary property in wet, below-grade commercial foundation applications.