This specification covers Grades G (granule surfaced) and S (smooth surfaced) prefabricated bituminous sheet materials reinforced with polyester fabric and modified by styrene butadiene styrene (SBS) thermoplastic elastomer, intended for use in the fabrication of multiple ply roofing and waterproofing membranes. The sheet materials shall meet dimensional requirements such as thickness and net mass per unit area, as well as physical requirements such as peak load before and after heat conditioning, elongation at peak load, ultimate elongation, tear strength, low temperature flexibility, dimensional stability, compound stability, and granule embedment.