This type of roof system uses modified bitumen membranes, which are factory-rolled products with rubberized or polymeric asphalt applied to one side at the factory. It can be installed by mopping on hot asphalt to adhere the membrane to the roof or, more commonly, by using a propane torch to heat the underside of the coating. Melting to a near-liquid, the membrane is then rolled onto the roof in a continuous operation.