Marmot's Wind River -10 Degree Down Sleeping Bag is the mummy bag that you'll crave when camping in cold weather. Whether you sleep cold and take it out in the shoulder seasons, take it up to higher altitudes, or camp through the winter, this bag is filled with 850-fill down that lofts to trap your body heat close to your body. A Down Defender treatment protects the down from collapsing when exposed to moisture, and the baffles are designed to minimize gaps that can create cold spots.