Ground Tarps go underneath the Berm and are typically 1 to 4 feet larger than the Berm itself. They are made from an 18.5 oz/sq. yd. polyester blended PVC. By placing the Ground Tarp down before you deploy your Ultra-Containment Berm, you can prevent punctures, tears, and rips from rocks or debris that may be underneath the Berm’s floor.