RUBEROID Mop Granule FR membrane is a fire-retarding modified bitumen membrane manufactured to stringent GAF specifications. Its core is a strong, resilient non-woven polyester mat that is coated with an inherently fire retardant SBS polymer-modified asphalt and surfaced with mineral granules. RUBEROID Mop Granule FR Membrane is designed for new roofing and reroofing applications where long-term roof system performance is specified.