The cover is made using a combination of advanced thermoplastic polyurethane TPU specially designed to keep your outdoor furniture dry and looking its best for years to come. Taking cues from performance mountaineering apparel, the cover is designed to breathe, allowing trapped vapor to escape while keeping the rain out. This solves the problem with fewer covers, which can trap moisture, causing mold and mildew. And finally, adjustable drawstring hem cords help keep covers secure on stormy days.