Modified Bitumen is a type of roofing that is an evolution of asphalt roofing. It is made from asphalt and a variety of modifiers and solvents. There are several ways of connecting pieces of this material. In a heat application process the seams are heated to melt the asphalt together and create a seal. There is also a cold-applied adhesive application process, and some self-adhesive forms of this system. This material is also referred to as APP or SBS.