Single-ply membranes are flexible sheets of compounded synthetic materials that are manufactured in a factory. There are three types of membranes: thermosets, thermoplastics, and modified bitumens. These materials provide strength, flexibility, and long-lasting durability. The advantages of pre-fabricated sheets are the consistency of the product quality, the versatility in their attachment methods, and therefore, their broader applicability. They are inherently flexible, used in a variety of attachment systems, and compounded for long lasting durability and watertight integrity for years of roof life.
Thermoset membranes are compounded from rubber polymers. The most commonly used polymer is EPDM (often referred to as "rubber roofing"). Thermoset membranes make successful roofing materials because they can withstand the potentially damaging effects of sunlight and most common chemicals generally found on roofs. The easiest way to identify a thermoset membrane is by its seams - it requires the use of adhesive, either liquid or tape, to form a watertight seal at the overlaps.
Thermoplastic membranes are based on plastic polymers. The most common thermoplastic is PVC (polyvinyl chloride) which has been made flexible through the inclusion of certain ingredients called plasticizers. Thermoplastic membranes are identified by seams that are formed using either heat or chemical welding. These seams are as strong or stronger than the membrane itself. Most thermoplastic membranes are manufactured to include a reinforcement layer, usually polyester or fiberglass, which provides increased strength and dimensional stability.
Modified bitumen membranes are hybrids that incorporate the high tech formulation and prefabrication advantages of single-ply with some of the traditional installation techniques used in built-up roofing. These materials are factory-fabricated layers of asphalt, "modified" using a rubber or plastic ingredient for increased flexibility, and combined with reinforcement for added strength and stability. There are two primary modifiers used today: aPP (atactic polypropylene) and SBS (styrene butadiene styrene). The type of modifier used may determine the method of sheet installation. Some are mopped down using hot asphalt and some use torches to melt the asphalt so that it flows onto the substrate. The seams are sealed by the same technique.