broadly , the present invention provides a thermoplastic vulcanizate which can be readily processed into sheeting material for covering a roof that is both flexible and highly elastic . where other thermoplastic elastomeric compositions have either been too stiff to act as roofing membranes or not processable due to their melt flow characteristics , the present thermoplastic vulcanizate employs a polypropylene random copolymer resin and a polyethylene random copolymer resin having about 10 to about 35 percent by weight α - olefin co - monomer units ; together with a compatibilizing rubber and a peroxide - based cross - linking agent , to provide an effective membrane for covering roofs .