Alpinists and thru-hikers reduce weight and maximize performance with a system approach to insulation. The Therm-a-Rest Navis Down Sleeping Bag is designed specifically for backcountry ounce counters who want to save weight by wearing their insulated jacket at night. Sewn-through construction in the upper half of the bag layers easily over a belay parka or a lightweight pullover. The Navis sleeping bag performs in a wide range of temperatures, from 25F to 45F (-4C to 7C), depending on the jacket it's combined with.