The Sea to Summit Circuit Down Sleeping Bag holds real warmth down to a genuinely cold 15degF rating, with a shaped collar and continuous down-filled draft tubes sealing off heat loss where it matters most. A hybrid box-baffle construction keeps the down from migrating and leaving cold spots, and the same wraparound zipper still opens the bag fully flat if a trip's temperature climbs mid-week. What Our Gearhead(R) Experts Are Saying:"I spent a night well below freezing in this and never felt a draft creep in at the collar or a cold spot form anywhere in the footbox. The down stayed put through the whole night instead of shifting toward one side of the bag."