Osprey viper 9 hydration packhigh energy activity requires keeping hydrated the viper 9 and integrated 25 litre hydraulics reservoir ensures that you can carry all the required gear and liquid to perform your best the reservoir is accessed via an asymmetric zip for quick and easy refills the reservoir incorporates a unique hydrostatic plate that maintains an anatomical shape but also keeps water pressure high for a smooth delivery of water osprey also solved the wandering hose issue with