The Eberlestock Spike Camp Duffel Bag is designed to integrate with the Just One pack. It can be zipped or clipped to the outside of the pack to increase the Just One to a 7,000 cubic inch pack. The duffel can also be carried inside the Just One for added protection from the elements. If you need more room in your Just One pack, or just want a little more weather protection, then the Spike Camp Duffel is what you need. Weighs 14 ounces empty.