a prefabricated asphalt - based waterproof roofing membrane for use in a multi - ply asphalt - based commercial roofing system , e . g . a cap sheet that forms the exposed layer of a multi - ply built - up roofing system , is manufactured at a factory to have a highly reflective non - asphalt based elastomeric top coating layer with an upper surface that meets current epa energy star requirements . preferably , a polymer primer layer is interposed between the highly reflective coating layer and an asphalt saturated and coated reinforcing substrate to keep oils and other colored components in the asphalt from exuding into the highly reflective coating layer .