Osprey Raptor 4 Hydration Lumbar Pack – Black. Off the back and leading the packOspreys premium mountain bike lumbar includes a 1.5-liter reservoir and features designed to keep you in the saddle. Dual hipbelt pockets on the Raptor 4 grant easy access to snacks and a stretch mesh front pocket keeps kneepads gloves or a light jacket handy. Side compression and a hip-wrapping backpanel stabilize the pack from techy climbs to the jump line.