The APP membrane, short for Atactic Polypropylene Membrane, is a special waterproofing material that is manufactured from Bitumen. They comes in rolls. The APP membrane is a very efficient and durable waterproofing material used in most constructions. It is a common waterproofing material used on concrete flat roofs (which are still roofs) or roofs with low pitch. Apart from concrete roofs and low pitched roofs, other areas of application are concrete gutters, basements and retaining walls.