May 06, 2022 · HDPE/Bentonite Sheet Membrane Dual Waterproofing System Paraseal GM/LG – 60 mil is a sheet waterproofing and methane-mitigating membrane nsisting of 60 mils of HDPE, expandable granular bentonite and a protective layer of spun-bonded polyester. The mposite weight of the sheet is up to 1.5 lb/ft², creating a dual waterproofing system.