Ready to go when you are Ready to go when you are the Osprey Viper 3 has an easily refillable 2.5 Litre Hydraulics reservoir & quick access pockets that allow you to have this backpack set to go before you know it. Osprey have designed this Viper with all the cool features of it bigger namesakes, Biostretch harness & Air Scape back panel designed for ventilation that will keep you cool, internal key attachments & pockets for the items we cant do without & lockable bite valve to prevent leakage. Easy to access fluids High Ventilation Organised Storage Description by Rebecca Solley, Rutland Cycling e Commerce Team