The NEMO Sonic 0 Sleeping Bag is a zero degree sleeping bag for cold weather sleeps in the mountains. Fish Aren't the only ones with gills these days, as this bag has Thermo Gills;, which helps regulate the internal temperature. Little warm? Open 'em up. Little cold, keep 'em closed. The 850 fill power down delivers the heat while compressing down for space saving in your pack. Features of the NEMO Sonic 0 Sleeping Bag Winner of a 2015 Backpacker magazine Editors' Choice Award, Sonic has been praised for being the only bag you really need from 0Adeg F to 40Adeg F Adjustable Thermo Gills allow you to control the internal temperature of the bag without letting in cold drafts, extending your comfort range by 20Adeg F or more Stretch construction at the knees helps maintain bag shape, thermal efficiency, andloft, while offering enhanced volume so you can sleep on your side or with your knees bent Thermo gills allow you to regulate the warmth of the bag on milder nights by as much as 20Adeg F/11Adeg C without letting cold drafts inside Stretch construction at the knees offers extra volume for side sleeping but keeps the bag close to your body for thermal efficiency Oversized draft collar Insotect flow vertical baffles Temperature regulating thermo gills closed Included Accessories: Cotton storage bag, drawstring stuff sack