My wife and I have slept in the bags twice now - once in the Oregon Blues at about 30 degrees and once in the Southern Utah desert at about 50 degrees. As you can imagine, the 50 degree night required using the bag open, as a blanket so we wouldn't overheat. My wife got a little chilly at 30 degrees, even with the bag fully zipped and her sweats on. But I stayed warm with just underwear. The bag is a little on the heavy side but a lot of bang for the buck. I have yet to sleep in it in cold weather but I would guess that I would stay comfortable down into the teens without having to put in a liner. I would strongly recommend it for someone looking for a bargain synthetic bag. The retail price doesn't come close to the best discounted prices of its competition.