Owens Corning® FOAMULAR® 250 Extruded Polystyrene (XPS) Insulation is a closed cell, moisture-resistant rigid foam board well suited to meet the needs for a wide variety of building applications. FOAMULAR® 250 XPS insulation is great for many residential and commercial construction applications such as wall furring, perimeter/foundation, cavity wall, pre-cast concrete, under slab, crawl spaces, sheathing and other applications.