Sleeping Bag Loft and Temp Rating


Auribus Teneo Lupum
Dec 27, 2012
I was not able to get any nights in really cold weather this year to test out my thickest sleeping bag. So I thought I would ask if anyone has experience in weather between -10F and -30F. How much loft do you need in a bag made of down fill to be reasonable comfortable? This is assuming of course a quality bag with baffles and a mummy hood.

I have done some research in cyber space on the interweb and it seems like they over state how warm a bag is going to be. I have only been down to 0 in a crappy synthetic bag and my full snow suit underneath several years ago. I was not a happy camper. I have since upgraded but have not been able to use my bag(s) in anything lower that +15.

Thanks in advance
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Though I have lived in areas that regularly got down to -40 on the Turtle Mountain Plateau, I don't have any first hand experience with camping in it, just hiking... LOL

but since nobody has answered your query I do have experience with Western Mountaineering bags and have three of them that seem to be close to their ratings to me anyway. Part of it is going to be how snug the bag fits and if it has a hood but you can get a glimpse with Western Mountaineering's charts of what they think. Usually they are considered fairly conservative in their ratings. The Cypress has 10.5 inches of loft and they rate it at -30. For me in a tent and a couple of closed cell foam pads underneath, maybe...

I have their Sequoia 5 degree bag and mostly use it for around 15 degrees. My 25 degree Sycamore gets more use because fall and spring are the seasons I like to be out and will look for milder weather and temps now. Both of those bags are wide taper, not mummy bags. Mummy shape will be easier for your body to keep warm but I like a roomy bag.
It seems that back in the day, most bag makers were more honest with their bag ratings. Maybe that's because I slept warmer then and a -5 F bag would keep me warm to -5 F. I remember reading how most reputable bag makers tested their bags using some device, a human like copper mannequin filled with warm water to see if their bag rated at whatever temp would actually keep it warm at that temp. I'm not sure if anyone uses that anymore. Anyway, back then, 10 inches of loft seemed to be the norm for minus 40. Some friends have -40 down bags for their spring treks up here and they seem to have about 10 inches of loft. My old -40 synthetic bag was in that neighborhood also. It was a NF mummy bag and so tight that I preferred not to use it. I would use my -20 and a fleece liner and be fine down to -40 or so.
Thanks guys. That's about what I was thinking. Thanks for your input. I have a few bags that range from 8-12 inches of loft. The thickest is an old Eddie Bauer Kara Karom that measures in @ 12". The down side is that it lacks baffles on the chest. I just hope I never have to test it out at or below -20.
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