These hydration packs are made of high-quality TPU flexible food grade material. The inside of hiking water bladder is smooth and able to keep the water clean. Double sealing lines on both edges makes water bladder backpack more pressure tolerant and safe, hence makes it leak proof water bottle.The mouthpiece is easily grabbable with your mouth. You can also comfortably bite the mouthpiece which makes you drink water smoothly. The hydration reservoir also has a shutoff bite valve that can automatically seal and prevent leakages.