Interior insulation jobs that use the wrong foam board end up with moisture problems, shrinkage gaps, or code violations that cost more to fix than the original substitution saved. Styrene foam board is a specific formulation for interior cavity and continuous insulation applications where it won't see the direct UV exposure or permanent below-grade saturation that extruded polystyrene is rated for. 1-1/2-inch thickness for interior wall cavity fills or continuous interior insulation where a higher R-value per inch than fiberglass is needed. The 4x8 sheet covers 32 sq-ft per board and works with standard framing layouts. Designed for interior use — install behind drywall or as a continuous insulation layer on interior walls where moisture management is handled by the wall assembly. Standar Stocked at Crofton Lumber and Akron Lumber.