The Atom 40degF Sleeping Bag is Marmots lightest bag. The perfect bag to take with you on any summer backpacking/climbing trip with its warmth to weight ratio being remarkable. The Atom also has a smooth feel like you are sleeping on silk sheets, which can definately help you on that summit push the next day. Filled with certified 850 Fill Goose Down, the best down in the market independently tested and certified by International Down and Feather Laboratory in Salt Lake City, Utah. Retested at fill time in Santa Rosa to ensure 850 fill power every time. Sewn through baffles makes the overall weight lighter and a side blocked below the end of the zipper keeps the down evenly distributed eliminating any cold spots that could occur.