STYROFOAM Brand Insulation from Dow Chemical Co., Midland, Mich., is an extruded polystyrene foam that is designed to resist water well and have a high insulation value. It is used in basement wall insulation and foundation drainage, slab-on-grade insulation, waterproofing/damproofing protection and radiant floor heating applications. It also is used in insulation applications for a wide variety of roofs and ceilings, and for all kinds of walls.