Nemo Equipment's Sonic 0 Down Sleeping Bag is our top choice for everything from hut trips in Colorado and Utah to winter camping in Montana. It performs well when temps dip down to single digits, and it's designed with a venting system that's a rarity in its class. Thermo Gill vents along the torso open up if things get too warm in our tent or hut, but this sleeping bag doesn't let any cold seep in if we forget to close them before shutting our eyes for the night. Nemo also uses 850-fill Power Down, which makes for a light and compressible, and highly warm, bag. To top it all off, the outer fabric is treated with a DWR finish to repel light moisture from snow and condensation.