About the Ortlieb Bikepacking Seat Pack The Ortlieb Seat Pack is a large and waterproof saddle bag with a secure and space saving roll top closure. Thanks to the roll top the volume of the bag can vary between 8 and 16.5 Litres. Working alongside the adjustable volume is the purge valve which allows any extra air in the bag to be released, which keeps the content of your seat pack together and and away from rattling. The Seat-Pack securely fastens to the seat post and saddle rails of almost any bike. Robust fabrics, custom stiffeners and an optimized strap design ensure the Seat-Pack performs in harsh off-road conditions and safely transports your gear. Weighing only 430g it is super lightweight. Key Features Suitable for carbon seat posts. Lightweight design. Four 3M scotchlite reflectors for various roll volumes. Ortlieb Seat Pack Instruction Manual