Polyglass APP Base is specially designed for use as a base ply or interply layer in mechanically attached or heat-welded applications. Polyglass APP Base can also be used as a base sheet for Self-Adhered systems. The top and bottom surfaces of the Polyglass APP Base are finished with poly film. It is an APP modified bitumen roofing membrane base sheet, reinforced with a fiberglass mat, saturated and coated with a polymerized asphaltic compound with exceptional waterproofing and weatherability.