Bitumen is a tacky, black and highly viscous liquid or semi-solid form of petroleum. The primary use of asphalt/bitumen is in road construction, where it is used as the glue or binder mixed with aggregate particles to create asphalt concrete. Its other main uses are for bituminous waterproofing products, including the production of waterproofing membranes and protection boards and for sealing flat roofs.

There are two general types of polymer modified bitumen membranes. Those with the principal modifier being atactic polypropylene (APP) and those with bitumen modified with styrene butadiene styrene (SBS). This polymer modified membranes differ in characteristics as well as application. Generally, APP modified bitumen possess the characteristic of a ‘plasticised asphalt’, whereas SBS polymer modified bitumens have a characteristic of ‘rubberised asphalt’.