Given how little it weighs, the Nathan Zelos Hydration Vest can carry a surprising amount of liquid refreshment for long hot weather runs. Apart from the two liter bladder in the back, the Zelos also has an included 18 ounce SpeedDraw Flask in one of the bottle holders, and an additional bottle holder can store another 18 ounces of liquid so you can run with a total of three liters distributed evenly around your torso. The vest's Propulsion Harness provides a three way adjustability to keep it stable so you can run without it bouncing around. Wall mesh shoulder straps leave your shoulders sweat free, and the back panel is perforated to bring some breathability to your back. The Zelos also features one zippered pocket for your smartphone, a stash pocket over one of the bottle pockets for gels, a pocket for electrolyte tablets, a gusseted stretch mesh rear pocket for a headlamp, an internal stash pocket for your keys and wallet, and a rear external shock cord to store an unneeded layer in the afternoon. Reflective trims make sure you stay visible when you get back into town after the sun sets.