SOPRALENE Flam 250 is composed of a proprietary formulation of elastomeric styrene-butadiene-styrene polymer modified bitumen and is reinforced with a tough, dimensionally stable non-woven polyester mat. The topside and underside are surfaced with polyolefin burn-off film to optimize heat welding. SOPRALENE Flam 250 is a SBS-modified bitumen base ply for use in approved multi-ply membrane & flashing assemblies.