Destined for long grinds up desolate forest roads and two-wheeled adventures crossing state lines the Ortlieb Seat Pack carries clothing protective outerwear personal hygiene items and mission-critical supplies while you're bikepacking down the trail and touring on the road. It's available in medium and large sizes for customizing your storage capacity. The medium size is ideal for mid-sized loads with its 11-liter capacity and the large supports bigger loads expanding from 8 to 16. 5 liters of storage space with its adjustable straps. Both seat pack sizes have roll-top closures to keep out the elements and are constructed from waterproof materials. The medium only needs 6 centimeters of post space available allowing you to use it with dropper posts and smaller frames with limited clearance. On the contrary the larger uses two straps so it needs 15 centimeters of available seatpost space to support these bigger loads. You'll find both attach to the seatpost rails for additional security and have adjustable straps to lessen overall bulk. Additionally the large has an external bungee for strapping down a jacket and the medium has a vertical daisy chain for attaching a rear safety light.