Torchflex TP-180-FF-Base Heat Welded Base Sheet is constructed using a tough non-woven reinforced polyester mat strengthened with select glass fiber strands. It is coated top and bottom with select SBS polymers and premium quality asphalt. A thin micro-perforated film covers both surfaces; the top film of the product will melt during the application of the heat welded cap sheet while the bottom film dissolves during heat welding to the substrate. Torchflex TP-180-FF-Base can be used as the “lay-flat” base sheet in a layered membrane construction system.