With its extruded polystyrene (XPS) construction, this board does not absorb water, is not a food source for mold, and is not subject to moisture-related damage and deterioration. An R-Value of 5.0 per inch of thickness makes it an excellent thermal insulator that increases the energy efficiency of your structures. And it retains its insulating properties over time. The board also provides an extra barrier against moisture infiltration. Choose between a square edge (CM) and an interlocking shiplap edge (SL) that helps reduce energy-robbing air leaks at seams and gaps. XPS Insulation Board is ideal for a variety of applications, including below slab, below grade along the foundation, inside basement walls, exterior insulation over wood sheathing, and residing.