This is a sleeping bag specially ordered by "west Niigata," a popular store for outdoor enthusiasts, from NANGA. While the original NANGA uses 40dn nylon taffeta, this version uses 20dn ripstop nylon. This thin, lightweight, and expensive fabric, typically used in ultralight models, significantly contributes to weight reduction. Additionally, the back, which gets compressed during use, features a single-quilt construction, while the top side uses a box-quilt construction. Even with the same amount of down, this design increases the down volume on the functional top side, enhancing warmth. The base model is the NANGA Down Bag 600STD. The comfort temperature is -2 degrees Celsius, making it suitable for three seasons. The limit temperature is -8 degrees Celsius. For reference, on Mt. Kumotori in mid-winter, the user wasn't cold even with an outer temperature of -13 degrees Celsius while wearing a down jacket. Also, in August on Mt. Tsubakuro, it was so hot that the user slept with their upper body outside the sleeping bag.