EPS beadboard handles moisture differently than extruded foam — it breathes, which means incidental moisture in cavity wall and floor slab applications doesn't get trapped and cause problems later. For insulation under concrete slabs or behind siding where condensation can happen during temperature swings, that's a meaningful difference in long-term performance. 3/4-inch board is the standard thickness for floor slab underlayment and above-grade cavity wall insulation where you want some vapor transmission. The 4x8 sheet covers 32 sq-ft per sheet with fewer seams to tape — fewer seams means fewer points where the thermal boundary can be compromised during the pour or install. Standard on insulation contractors and masons across northeast Nebraska and northwest Iowa who deal with the humidi Stocked at Crofton Lumber and Akron Lumber.