evo.com | Osprey Fanny Packs > With 4 liters of carrying capacity, the Osprey Seral 4 Lumbar Pack is the optimal size for the vast majority of mountain bike rides. Equipped with a 1.5L hydration reservoir, a big zippered main compartment with internal organization for bike tools, and Osprey's beloved AirScape lumbar backpanel for ergonomic comfort and ventilation, the Seral 4 Lumbar Pack is just what you need to focus more on the trail and less on combating sweaty back syndrome. 7.5" H x 12.5" W x 4.5" D Blinker Light Attachment with Reflective Graphic Large Zippered Main Compartment with Reservoir Sleeve Main Compartment Tool Organization Main bluesign(R) approved 600D recycled PET polyester, PFC-free DWR | Osprey Seral 4 Lumbar Pack 2026 - O/S in Black | Polyester