I never believed it until I slept my first night in below-freezing temps. . . but the sleeping bag is more than enough. The pockets along the bottom (three on each side) hold a layer of air. I'll stuff the water bottles and my camp moccasins into them to expand the air pocket some and to keep my water from icing up. Since I sleep in my first two layers of clothing, that plus the bag is more than enough to keep me toasty. The first time I slept in a fleece sweatshirt, I woke up too hot and had to take it off. Ended up using it as a pillow.

One exception is on really cold nights, my toes will get cold. The pockets don't extend the full length of the hammock and so from about the knees down it feels colder. I remedy that by wearing my extra pair of socks to bed. Problem solved.