The Rightline Gear Sport 3 Car Top Carrier is 100% waterproof and attaches to vehicles WITH or WITHOUT a roof rack. Attach the carriers straps to a vehicles roof rack or use the Car Clips to attach the straps to a vehicles door frame weather molding. The carrier is made from UV protected PVC Semi-Coated Mesh XT and Hydrotuff for maximum durability. The materials are sewn together for strength and then welded along the stitching to make the seam waterproof. The carriers ZipRight System locates a urethane coated zipper on the protective zipper flap where water cannot enter. The Sport 3 is one of the largest car top bags on the market and aerodynamically designed to save $$$ at the gas pump.