Think of it as a hydration jet pack The Nathan Synergy race vest is engineered to enhance your maximum velocity. Propulsion Harness moves in harmony with the movement of your shoulders and upper back, reducing wasted energy. Honeycomb 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 the 100 fl. oz. reservoir. Hydration reservoir features a separate chamber for electrolytes potency dial allows you to control the ratio: all water, all electrolyte or a combination of the 2. Bite valve is bent at 90deg and can be easily shut off with a quick twist. Zippered main compartment hols up to 750 cu. in. of gear. Dual front pockets-1 mesh holster and 1 zippered. Stretchy back pocket holds a jacket or gloves. 2 mesh side pockets hold water bottles or other small items.