These covers are 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, WeatherX covers are designed to breathe, allowing trapped vapor to escape while keeping rain out. This solves the problem with lesser covers, which can trap moisture, causing mold and mildew. And finally, adjustable drawstring hem cords help keep covers secure on stormy days.