Modified bitumen, also known as modified asphalt or just asphalt, is a type of roofing material made of asphalt combined with polymerized rubber or plastic. It is reinforced with fiberglass to create a rugged-yet-flexible waterproof membrane primarily used on flat commercial roofs.
Depending on the type of material and whether a second layer is installed, these membranes may be installed as part of a two-layer system or a multi-ply system.
It has become one of the most common commercial roofing materials because it is easy to install and offers long-term durability, at an affordable price.