After the waterproofing membrane is applied to the foundation, protect it from damage during backfilling with PB4 Waterproofing Protection Board. This durable extruded polystyrene (XPS) board has the compressive strength and impact resistance to withstand even the toughest load pressures. Its dense, closed-cell construction and tough plastic facers resist both moisture absorption and decomposition from long-term exposure to chemicals in the soil.