FOAMULAR 250 Extruded Polystyrene (XPS) rigid foam insulation for exterior walls contains hundreds of millions of densely packed air cells to provide exceptional thermal performance. Its also virtually impervious to moisture, preventing loss of R-value due to moisture penetration. FOAMULAR weighs considerably less than plywood, OSB or other non-insulation material so it's easier, faster and safer to install. Plus, the product's built-in rigidity means it can be scored and snapped, cut, or sawed with common tools. Sagging and settling are never a problem.