Waterproof Band 5x98A modified polyethylene (PEVA) core with a non woven polypropylene on both sides Provides protection of the substrate from moisture penetration This waterproof membrane is 5 mil thick and has a water vapor permeance of 0. 051 perms, when tested according to ASTM E96, using Procedure E at 90% relative humidity Made from the same lightweight, waterproof material as the waterproofing membrane and is for use over horizontal and vertical seams.