Membrane roofing is used on buildings with flat or nearly flat roofing. Membrane roofing is factory-fabricated, easy to install, and very lightweight. Because membrane roofing is tough and resistant to abuse, it is commonly used in commercial application, and is increasingly common in residential application. Membrane roofing is typically made from synthetic rubber or thermoplastic (referred to as single-ply Synthetic Rubber (Thermoset) is made of large, flat pieces of synthetic rubber or similar materials. These pieces are welded together at the seams to form one continuous membrane. Thermoplastic Membrane is similar to synthetic rubber, but the seams do not form a continuous membrane. The 'lap' seams are bonded (melted or dissolved) with heat or solvents, and can be as strong as the rest of the membrane. This eliminates much of the leakage concerns associated with flat roofing systems. Membrane can be patched relatively easily, and breaks and leaks are easy to locate. Newer types of membrane roofing systems contain materials that resist expansion and contraction, as well as reflect UV rays. Also, because these membranes lack seams or have very strong seams, what expansion and contraction does occur does not create leaks and breaks at these seams.