COMPCOOLER Cooling Backpack with internal cooling channel and double chambers 2.5L Hydration detachable Bladder. Hydration Cooling Backpack ( Double layers backpack with internal cooling channel, Pump unit, 3L Bladder, Battery and charger). Compcooler Hydration Cooling Backpack (HCB) is made up of Cooling backpack, 3L double chambers bladder, one chamber for water circulation, the other chamber for cold water hydration. Mini pump circulates the cold water go through the cooling channel embedded on the rear of backpack and strap, air permeability mesh liner provides better skin touch feeling. 3L ICE block provides up to 6 hours cooling, cooling temperature range 46degree F-68degree F(7degree C-20degree C), ambient up to 140degree F(60degree C), widen strap design provides perfect body cooling performance, quick release bladder, easy to extend cooling time, 100% physical cooling, safety and healthy. Perfect cooling performance, quick operation, comfort to wear, this model is good for outer application. It looks like a regular backpack with internal cooling liner. Features: Compcooler Hydration Cooling Backpack (HCB) is made up of Cooling backpack 3L double chambers bladder, one chamber for water circulation, the other chamber for cold water hydration Mini pump circulates the cold water go through the cooling channel embedded on the rear of backpack and strap, air permeability mesh liner provides better skin touch feeling 3L ICE block provides up to 6 hours cooling, cooling temperature range 46degree F-68degree F(7degree C-20degree C), ambient up to 140degree F(60degree C), widen strap design provides perfect body cooling performance, quick release bladder, easy to extend cooling time, 100% physical cooling, safety and healthy Perfect cooling performance, quick operation, comfort to wear, this model is good for outer application