The Endurance Pack is a fantastic piece of gear to take you a long ways. But when the weather turns terrible, your gear requirements are larger, or if you just want to have the ability to hold more gear, we have a solution for you. This add on pack creates an additional 4 Liters of storage to the rear of the pack. It attaches via webbing at the top, and through the nylon web at the bottom. It's best for light jackets and layers, not heavy bulky items.