Features (from REI site): -Harness moves in harmony with your shoulder and upper-back movements, reducing wasted energy -Mesh shoulder straps and back panel channel air across your skin and wick moisture away to improve overall comfort -Insulated reservoir compartment zips open and provides quick, easy access to 2-liter reservoir (included) -Bite Me™ valve is bent at a 90° angle; can be easily shut off with a quick twist -Dual front pockets include one that's zippered to secure keys, ID or cash while the other stashes energy gels in a stretchy mesh pocket -2 zippered rear compartments organize additional items A review: https://www.outdoorgearlab.com/reviews/fitness/hydration-pack-for-running/nathan-hpl-020