The Nemo Sonic is the most comfortable bag in our review. It has a super wide cut, a little stretch around the footbox, a big hood, and comes loaded with unique features. Our testers could toss and turn throughout the night to their heart's content. We achieved sublime slumber in all positions, whether flat on our backs, prone, or even curled up in a ball. All this at a weight and compressibility equal or greater than 8 of the other cold weather down bags in this category. The Nemo Sonic receives our Top Pick for Comfort. It lost points in the warmth metric for the same reasons it did so well in comfort. There's lots of space to move around in, which equals less insulated space between the sleeper and the freezing cold. Additionally, this bag has less down than eight of the other bags. For a warmer bag that's nearly as comfortable, check out the Mountain Hardwear Phantom Torch 3.
With the success of the Sonic 0, NEMO decided to add another bag to the lineup: the NEMO Sonic 15. Retailing for the reduced $430, the Sonic 15 has the same features as the Sonic 0, making it the perfect choice for those looking for an extremely comfortable bag but who don't need all the extra fluff.