Note: The hydration bladder has been installed in the inner layer of the backpack. 3L Hydration Bladder: Removable water reservoir with an enlarged filling opening is included. Made of EVA material. Its wide opening makes it easy to clean and add ice cubes. The ON/OFF valve helps adjust water flow and prevent leakage. 2 Functional Compartments: The main pocket contains a 3L/106oz hydration bladder with a large opening and a smaller one connecting the smart hose. The back layer for storing personal belongings such as mobile phone, wallet, keys, and so on. Comfortable Design: Two adjustable shoulder straps and a safety strap keep the hydration backpack on your back and reduce bouncing, making it fit perfectly on shoulders, chest, and waist. Suitable for men and women. Good Quality Material: This hydration backpack weighs only 0.8 lb. Made of high-density 900D Oxford fabric, lightweight and durable. The soft back panel keeps your back comfortable and breathable when wearing it during outdoor activities. Versatility: Hydration backpacks will be an excellent partner for hiking, cycling, running, skiing, climbing, hunting, and any short trips.