Large Capacity: Features on a mian compatment storing max. 2L water bladder(not included),a front open pocket,two side drawstring pockets and two small side zipper pockets. Lightweight & Breathable: (Only 0.5lbs)Made with lightweight polyester materials for durabuility.Excellent air ventilation system consist of mesh back and adjustable wide mesh shoulder straps,prevents stuffiness and distributes weight effectively.And flexible sternum straps reduce strength consumption. Safe: Reflective strips around the bag provides more safety during nighttime activities. Convenient: The hydration backpack with two sides water pipe outlets,easy to drink water without taking the backpack off or stopping your steps.Convenient whistles for enmergency sistuations. Wide Application: Suitable for cycling,camping,hiking,mountaineering,biking,running and other outdoor activities. This hydration backpack makes it easy to drink water directly without taking the backpack off or stopping your steps.Suitable for riding,cycling,running and mountaineering etc. Specification: Material: Polyester Size: 37 * 19 * 1 cm / 15.3 * 6.6 * 0.4 in Capacity: 2.5 L (just store your max. 2L water bladder) Weight: Approx. 240 g / 0.5 lb Package List: 1* Backpack This hydration backpack makes it easy to drink water directly without taking the backpack off or stopping your steps.Suitable for riding,cycling,running and mountaineering etc. Specification: Material: Polyester Size: 37 * 19 * 1 cm / 15.3 * 6.6 * 0.4 in Capacity: 2.5 L (just store your max. 2L water bladder) Weight: Approx. 240 g / 0.5 lb Package List: 1* Backpack