Armourvent Base Self-Adhering Base Sheet is composed of an inorganic reinforcing mat of high strength non-woven glass fibers and features a unique pattern of discontinuous modified bituminous strips to aid in vapour diffusion of moisture below the membrane. The top surface of the product includes a self-adhering selvage lap, finished with a micro-perforated film to allow heat welding application of the cap sheet. The patterned bottom surface is self-adhering with a release film. Armourvent Base is specially designed for partial adhesion to the roof substrate to minimize roofing system blisters that may form due to un-vented moisture build-up.