SODIAL(R) 3L Hydration Water Bag Pouch Backpack Bladder for Hiking Climbing Survival Constructed by waterproof 600D high density Nylon material. Two layers cargo design, one for hydration bladder, and the other for extra carrying purpose. Adjustable shoulder strap and chest belt, suitable for heavy carrying. Equipped with a tube with a bite valve to drink, so you don't need to hold it to drink. A switch on/off bite valve, convenient for control the flow of water.