The Osprey VIPER 9 multifunctional backpack with a water reservoir of 2.5 litres. Viper 9 is a great backpack for full-day bicycle trips, trail running or for your walks in the countryside. It is equipped with many Osprey technologies that ensure comfort and organize your belongings perfectly. The 2.5-litre Hydraulics hydration bladder and magnetic mouth piece holder mean never having to worry about thirst again.