Vktech 2.5L/3L Tactical Outdoor Hydration Water Backpack Bag with Bladder 6 Colors Constructed by waterproof 900D 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