Coverking Presidium Class A RV-cover is an outstanding value and provides amazing protection for your RV. Made from 600-denier polyester the cover is rougher and thicker than the average universal RV-cover. The 600 number refers to a type of polyester thread count in one-inch intervals (the higher the thread count the tougher it is). All seams use an advance double-stitched method to ensure that covers remain water-resistant even at the closure. The cover is also quite breathable to ensure that moisture is kept out of the cover. Ventilated air-flats are also aligned around the top edge to reduce wind friction and to prevent moisture buildup. The cover also comes with built in zippered-door-flap for easier in and out access. To keep the RV-cover in place included are adjustable buckles integrated on opposite ends.