FUNCTIONAL HYDRATION: Our 4 liter running vest keeps you hydrated on every run for peak performance. There's plenty of storage for hydration and essentials with 2 water-resistant pockets, 2 kangaroo pockets, and a new shape for breathability. INSPIRED BY THE JOURNEY: Nathan hydration vests deliver on what matters through intuitive design, comfort, quality, and smart storage. This 4 liter running hydration pack with bladder helps runners improve mile after mile and year after year. SIZING & FIT: Unisex sizing and fits different body types, no matter how you get active. This Nathan hydration vest is designed like a second-skin with a chafe-free fit and form. 20% lighter than the Krar and Howe Vests. SPECS: Runner vest weight without bladder: 6.1oz; Weight with bladder: 12.0oz; Storage capacity: 4 Liters (244 cu in). Running hydration vest comes with two 20oz hydration soft flasks. ESSENTIAL DESIGN: This running water vest is designed with moisture wicking tapered back panels so you can run chafe-free. New side pocket for easy access, vertical pocket, and two 20oz hydration soft flasks with ExoSpine for stability