The only way to achieve 10” of STYROFOAM™ Brand insulation is to combine 3 layers of using 2”, 3” and/or 4” sheets. STYROFOAM™ sheets are available up to 4” thick. If obtaining the 10” of insulation in a single layer is desired, then EPS would be used. Expanded polystyrene can be purchased in any thickness and in a variety of R-values making it a cost effective alternative to STYROFOAM™ insulation.