WATERPROOF – Your luggage will be well protected by 600D heavy duty PVC coated tarpaulin. All seams are heat welded rather than stitched with thread. It's thicker, more durable and waterproof than Oxford cloth with PVC coating or PU glue. For the best waterproof effect, we use WATERPROOF ZIPPERS instead of common zippers and add 8 hook & loop tapes to fix the 10 cm wide zipper flap. SAFETY - It's dangerous to let straps go through the interior of car because they may interfere the popping of side curtain airbags. To prevent that, we offer 6 door hooks for the cars without roof racks to secure the straps. In addition, we add 4 reinforced patches between each strap and the bag to increase the connection strength. Without the reinforced patches, the straps are more easily tore down and the bag may fly to the car behind while driving. SILENT - With the 2 lashing straps included, you can tighten roof cargo carrier to further keep your luggage secure and reduce noise. There is a cinch strap on each rack strap. Please use cinch straps to fasten excess straps to prevent noise caused by excess straps tapping car while driving. UNIVERSAL DESIGN - Whether the vehicle has roof rack or not, the door hooks and rack straps make car top carrier bag quickly and easily installed. NOTE: If your vehicle doesn’t have roof rack, please make sure the weather strips can be peeled away and the car doors are not sliding-doors. GUARANTEE - 1 year warranty for the cargo bag if it's damaged or not weatherproof anymore. Please contact us to get the after-sale and we will make it right by refunding or replacing your order.