The APP membrane is a special waterproofing material made from Bitumen. A polypropylene membrane is used as reinforcement material to prevent the bituminous layer from cracking during expansion & contraction of roof slab due to diurnal heating & cooling. The polymer modified bitumen used allows a more viscous and less temperature sensitive bituminous material. The polypropylene backing increases the tensile strength of the waterproof layer and its resistance to acidic soils.