The manufacturers' state that the ratings are assuming a person is wearing long underwear, socks and head covering. Now, I don't always sleep that way when hiking but I recently got a chance to test my Hugger#5 bag in the low 40's. I wore exactly what was recommended and I got chilly. The low for the night was 39 degrees. Around that time, I had to put on a light down jacket to stay warm. I just don't think they put enough down in the this bag. I think it should be rated as a 45 degree bag.

I've owned this bag for 2 years and it is just plain awesome. I sleep cold but I've had this bag down to 13 degrees and it kept me toasty warm. The stretch feature is perfect for me, too. I hike/camp with an 11 yo old dachsund dog who's cold natured so she always climbs in the bag with me. We couldn't be more comfortable. No other mummy bags I've tried have enough inside for both of us. The Montbell is just perfect. I own 2, the #1 hugger for cold weather and the #5 hugger for warmer nights.

This is the only bag for me (us). I've only used it in temps down in the mid 30's so far but I'm always toasty warm and I'm a cold sleeper. I searched far and wide to find a high tech bag that wasn't the standard width because my little dachsund, wiener dog hikes with me and she insists on crawling inside the bag at night. With the Super Stretch, No other bag on the market affords the luxury that this bag offers. The stretchiness allows my dog and I to move around inside this bag with no problem. With other bags, I couldn't even zip them up with her inside. In a word, this bag is "Perfect!"