Large main compartment holds a 2-liter water reservoir. Easy-access reservoir opening is easy to fill and accepts most brands of water filters. Hands-free reservoir pressure valve. * Insulated water tube cover prevents water from freezing in the tube. Tuck-away mesh sport flap is hidden in a zippered pocket and holds a helmet. * Zippered front accessory pocket holds bicycle tools, accessories, or CD/MP3 player. Mesh front pocket and monster hook * Vapel mesh Airflow padded back wicks moisture. Vapel mesh Airflow adjustable shoulder straps. Adjustable waist belt secures the pack. Adjustable waist belt secures the pack. Reflective loop holds a bike LED blinker * Size: 17.25" x 9.0" x 2.0" Capacity: 138.0 cubic-Inch Weight: 2.17 lbs. Materials: Waffle Weave