8mm Cavity Drain Membrane for Basement Walls, Floors & Vaulted Soffits. Newton 508 is our high quality BBA cavity drain waterproofing membrane suitable for use internally below the ground to retaining walls, vaulted soffits and floors. Newton 508 is our flagship membrane and one of the most specified cavity drain membrane in the UK. The 0.7mm thick HDPE product allows for large industrial loads to be applied and the in line studs allow for quick installation with minimal surface preparation. Newton 508 is available in roll sizes 2.4m x 20m - 48m (M1) and 2m x 20m - 40m (M2)