The Snugpak Expanda Panel Summer is compatible with Snugpak Softie 3 Merlin, Softie 6 Kestrel, Softie 9 Hawk, and the Softie Tactical 2 sleeping bags. The sleeping bag panel is a zip in wedge that adds 16 inches of chest room to the sleeping bag and tapers gradually to the foot of the bag. The Expanda Panel Summer is equipped with Softie Premier synthetic insulation, which is washable and provides superior heat retention. The randomized fine filament fibers of Softie Premier insulation trap warm air to retain heat even when thoroughly wet. Softie Premier insulation does not lose thermal characteristics over time, even when stored in the compression stuff sack for long periods of time without use. The Expanda Panel Summer also features Paratex Steelplate as the outer shell to provide a breathable, water wicking, water repellent, and windproof sleeping bag panel. The inner lining of the expander panel is constructed with Paratex Light, a durable, windproof, breathable lightweight fabric that provides an efficient water wicking system to keep you warm and dry. The Expanda Panel Summer comes with its own convenient stuff sack and weighs only 11 ounces. The Expanda Panel Summer will provide additional room for you in your sleeping bag without compromising its practical thermal properties.