Shield Membrane: Shield Membrane is made of Thermoplastic Polyurethane (TPU). TPU was first developed in 1937. The material is renowned for many things including its: high elongation and tensile strength; its elasticity; and to varying degrees, its ability to resist oil, grease, solvents, chemicals and abrasion. A special property about TPU is its segmented structure, which is composed of hard segments (HSs) and soft segments (SSs). As temperature rises, the soft segments expand and tiny pores are formed on the membrane allowing water molecules to go through. In cold weather however, SSs tighten up and close up those pores. Consequently the strength and the insulation properties of the material increase dramatically, which helps to keep the wind and dirt from entering the cover and minimizes the chance of wear and tear by wind and cold weather extending the life of the cover. At Hentex we developed a special process laminating TPU to the outer and inner shell creating the SHIELD outdoor cover.