Woven and laminated to resist tears Treated to resist damage from the sun's ultraviolet rays Rotproof, waterproof and mildew-proof Lightweight--easy to handle and store. Rope-reinforced hem, double-stitched for strength, heat-sealed seams. Won't crack even in frigid temperatures. Rustproof grommets approx. 3 ft. apart. Reinforced corners on large sizes. Washable. Cannot be shipped express.