?The Seat-Pack is a spacious and waterproof Saddle-Bag with roll closure; its volume adjusts between 8 L (488 cu.in.) and 16.5 L (1007 cu.in.). An additional purge valve allows air to escape making tight packing easy. 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. With only 430 g/ 15.2 oz. it is super lightweight.