CertainTeed's Black Diamond Base Sheet is a heat-activated self-adhering, SBS modified, fiber glass base sheet with fine particle surfacing. It is intended for use beneath mopped and torched cap and ply sheets. Black Diamond Base Sheet may also be used as a vapor retarder under roof insulation. Provides additional strength, improved handling, pliability, and moisture resistance when used as the first ply over non-nailable and insulated substrates.