GAF SA Vapor Retarder is an SBS modified bitumen vapor retarder for use in approved GAF roof assemblies. GAF SA Vapor Retarder is composed of a proprietary formulation of elastomeric styrene-butadiene-styrene (SBS) polymer modified bitumen in combination with a high tack self-adhesive. The topside is surfaced with high-strength trilaminate polyethylene film and the underside is surfaced with protective polyolefin release film that is removed during application.