The two external layers of these Classic SFS covers are comprised of high tech spun-bond polypropylene, and treated with a UV compound. The internal layer of protection is derived from a sturdy waterproof and breathable material. These three layers, used in combination, offer a defensive covering that will fortify and protect all of your patio furniture. A unique buckle and strap system is an added feature that helps to further secure your patio furniture, even in the windiest conditions. Because it is breathable, moisture will evaporate through the material itself so mold and mildew build up is no longer a threat.