Foundation insulation that fails means cold basements and higher heating bills you can't explain to the customer. Expanded bead polystyrene handles ground-level moisture better than extruded foam in below-grade applications — the bead structure lets any incidental moisture escape rather than pool and degrade performance over time. 2-inch thickness gives you the depth needed for frost-line protection and basement wall insulation in this climate zone. The 4x8 sheet covers 32 sq-ft per pass, and the board format is easier to cut and install than batt insulation in below-grade work where the ground moisture conditions are unpredictable season to season. Standard on foundation and concrete contractors across northeast Nebraska and northwest Iowa — what gets specified for rim joist insulation an Stocked at Crofton Lumber and Akron Lumber.