The osprey viper 13l hydration pack is the ideal all round backpack that you can use for a long ride on the weekend or a quick commute to work the viper 13 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 de