This is a Camelbak Hydration Pack known as the Hydrobak, model 1737001000.
Built for the rigors for of daily use" the HydroBak is an economical hydration solution that is ergonomic and versatile. The included 1.5L" 50oz Mil Spec Crux Reservoir delivers 25% more water.
Features:
Rear Reservoir Access Flap
Front Zip Pocket Holds Your Small Essentials
Ideal for Light and Fast Jobs