Modified bitumen roofing is a factory-manufactured membrane that is provided in rolls, which are adhered to the substrate in either hot asphalt, cold adhesive or heat applied applications.  This type of roof system reduces stress on the membrane prior to installation.  There are two types of modified bitumen roofs: SBS (Rubber Modifier) and APP (Plastic Modifier).

• SBS (Styrene Butadiene Styrene "Rubber" Modifier) - SBS products are typically installed using hot asphalt as the bonding adhesive.  They can also be installed in compatible, low-solvent cold adhesives.  SBS roofs provide a broad range of formulations and mat composites for varying degrees of strength, elasticity and flexibility.  Many of the roofs are available with fire-retardant chemicals.
• APP (Atactyc Polypropylene "Plastic" Modifier) - APP membranes provide unsurpassed tensile strength while maintaining critical flexibility even in the coldest environments.  Typically, the back coating of APP modified asphalt is heated to a point where the bitumen acts as an adhesive, bonding the sheet to a substrate and bonding the overlapping edges.  There are, however, newer versions of APP modified that are now being installed in cold adhesives.