Online product description says this is rated down to 0F. When I received the bag, the label stated a "comfort" temperature down to 6F. My own experience at a week in temperatures around 25-35F really seemed to suggest a comfort temperature of 20F or so.Now I realize temperature ratings are pretty nonstandard and arbitrary. Still, at 25-35F wearing a tshirt and long-sleeve underwear top and compression boxers and soft-shell pants on a high-R value ridge-rest with a boiling-hot nalgene at the bottom, I was only moderately warm when the bag was fully zipped up. I'd have a very hard time expecting to remain comfortable down to 0F or 6F without adding more layers. I generally run warm in most sleeping bags.Your miles may vary, but it seems a bit odd to drop this much money on a bag that's just not that warm. It is pretty light, but it ships without a compression sack, so it takes up a bit of space. Construction is otherwise pretty decent and it seems durable.