SOPRAFIX Base 611 is a SBS-modified bitumen base ply for use in approved multi-ply membrane and flashing assemblies and is designed specifically for mechanical attachment to approved substrates. The underside is surfaced with fine mineral aggregate and the topside surfaced with polyolefin burn-off film to optimize heat welding. It is composed of a proprietary formulation of elastomeric styrene-butadiene-styrene (SBS) polymer modified bitumen and is reinforced with tough, dimensionally stable non-woven polyester mat engineered for mechanical attachment.