Modified bitumen is considered the evolutionary cousin of built-up roofing systems (BUR), which have been used on low-slope roofs for over 100 years. It is made of asphalt combined with polymerized rubber or plastic, then reinforced with fiberglass to create a rugged yet flexible waterproof membrane.

Modified bitumen roofing is primarily used on flat or low-slope commercial roofs. These membranes may be installed as part of a two-layer system or as part of a multi-ply system, depending on the type and material.