Moving fast and light in the backcountry doesn't mean you can ignore the weather. Despite its unbelievably low weight, the Mountain Hardwear Mtn Speed Down Sleeping Bag is rated at a versatile 32 degrees, which is plenty warm for spring, summer, and fall camping in most areas of the US. The reason for the low temperature rating and low weight is super high quality 850 fill power goose down, which is treated with Mountain Hardwear's innovative Q. Shield water repellant. Q. Shield is used on the down fibers to maintain the down's insulating properties if the down gets wet, so the days of using synthetic bags in wet areas are over.