Use the same material as outdoor waterproof dive bags - 500D double-sided PVC waterproof material, stronger and more waterproof than ordinary 600D polyester or Oxford cloth bags. Not only that, made of thick PVC net clamping cloth to ensure it is airtight, watertight, and durable. Comes with a detachable shoulder strap and double buckle on the back. The backpack also can be fixed on the rear rack while cycling.