CamelBak Volt 13 LR Hydration Backpack - 600cu in Fabric 4-point adjustable harness offers a custom, secure fit Lightweight back panel incorporates a vertical ventilation chimney, allowing your back to breathe LR designation stands for Lumbar Reservoir, placing the reservoir low and close to your body for enhanced stability Big Bite valve is ergonomically positioned for easy drinking It's easy to access the reservoir via the zippered flap at bottom front of the pack; simply lift the flap to unzip it, open the reservoir mouth and fill