3mm Cavity Drain Membrane for Basement Walls Floors & Vaulted Soffits. Newton 503 is a BBA approved cavity drain waterproofing membrane suitable for use internally to retaining walls, vaulted soffits and floors. Newton 503 is a flexible HDPE membrane which at 0.5mm in thickness provides a low profile drainage solution within the Newton Cavity Drain membrane range. Newton 503 (M5) is available in rolls 2m x 20m - 40m
