STYROFOAM™ Brand Square Edge Insulation 25 PSI is an extruded polystyrene foam insulation board that meets the needs of the commercial foundation and building floor slab market. This insulation can also be used for attics, foundations/slabs or crawl spaces in residential applications. It has 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. STYROFOAM Brand Square Edge Insulation is a type IV extruded polystyrene foam insulation with squares edges on all sides.