ratings for sub-zero sleeping bags

4:40 p.m. on January 10, 2011 (EST)
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so i'm curious whether there is any science to support that EN ratings diminish in accuracy at temperatures below zero.  Mountain Hardwear seems to think so; their literature says they only apply EN ratings to sleeping bags rated above zero.  Marmot says their bags are rated to the lower (but not the extreme) limit.  in other words, a -20 f marmot bag has an EN comfort rating somewhat higher, a lower rating of -20, and an extreme rating that's somewhat lower temperature.

also, is it fair to compare fill and bag weights for bags that are not EN rated? not clear that western mountaineering has adopted EN 13537.  so is it fair to compare their fill weights (assuming all 800+ goose down is roughly the same) to the companies that have adopted and do a good job with winter bags, eg Valandre, marmot, north face? or is there some reason it wouldn't be fair to do this kind of comparison?  i don't think a standard rating system is the last word, but until i can get winter bags and test them in a freezer, it can be hard to judge. 

i'm contemplating, after a long time, getting a down bag to replace my northface darkstar - a great synthetic bag, but it has seen a lot of service & is a real pain to pack, even with a compression stuff sack.  mostly looking at the marmot col or CWM, and mountain hardwear ghost.  i suppose some of the others (valandre, WM, Feathered Friends) may make a better bag, but they don't discount much or often.    

thanks for your thoughts - about the general questions, and about these three bags in particular.  i'm pretty convinced that either of these bags would fit my needs, but i'm open to criticism.

8:13 p.m. on January 10, 2011 (EST)
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I feel for ya-

With all the push for weight, I don't trust anybodys ratings.

My current 3 season bag packs down to 5"x 10" (no kidding) and they had the stones to label it a neg. 5C bag (23F)- EN rated, they claim-

I saw how tiny and light the bag was, and fell for the numbers. I am a hardy soul, and my bag would be realistic in the 40's (F) stand alone, not supplemented (tent/space blanket, etc.)

I would say that it is probably safe to compare weight and fill to determine the bag's capabilities, EN rated or otherwise IMO. 

11:28 a.m. on January 11, 2011 (EST)
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Never trust the temp rating for any bag - use reviews from actual users to get an idea of the bag's performance. Some people are cold sleepers, some people are hot sleepers. Take an average of the reviews that say it is warm enough, or it is too cold, and see if it would fit your needs. A good rule of thumb is to get a bag that is rated 10* colder then what you think you'll encounter. Also take into account air temp is different than wind chill, since a tent or shelter will block wind. My bag, for example, is rated   -20F. The places I climb may see temps with the wind chill close to -50F on a weekly basis, but the actual air temp rarely dips below -11F. Since my bag is also windproof and waterproof, it would block that windchill and hopefully keep me warm enough.

Here's the catch. At those temperatures, no matter what bag you use, you will never be comfortable. It's a matter of making it more bearable and preventing your death. So again, ratings are really not well understood - just because a bag is rated to -20, doesn't mean you'll be comfortable in -20F temps - it just means you hopefully won't get hypothermia.

I just added a review for the High Peak Mt Rainier -20 bag in the review section. I haven't tested it to the extremes yet, but have been in it in temperatures as low as 18, and was sweating.

It doesn't pack terribly small, but it fits in my pack's bag compartment. It is a hefty weight, like most bags that are rated below 0 - it weighs 5.5 lbs or so.

Best of all - it costs around $100.

My father in law is a butcher, and I would love to test my bag for a few hours in one of his meat freezers that is below 0 - I'll let everyone know if I actually do it.

11:47 a.m. on January 11, 2011 (EST)
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There's no good way of seeing this. To be frank, comparing fill and weight is probably the best way do get a general idea. Marmot all range their bag the way you described as do most of the other compagnies. The push for weight is alwas an issue but I dont think that the compagnies are trying to sell us scrap. (Althought, some might;-). You should see if there are any rental possibilities in your area. Following rating, especially in down bags of any tepmperature, can be troublesome. Some people have one bad experience and then sink the product, when in reality they had no idea what they were doing in the first place. Down bags, in my experience, are capricious thing that need to be treated with great care and attention. Good luck, wish I could help you more, but they are too many variables. I have a Marmot CWM and would not trade it for nothing.

7:22 p.m. on January 11, 2011 (EST)
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Thanks, all.  i appreciate the advice.  For what it's worth, some facts to chew on.  clearly, ounces of fill isn't the end of the story, but it's a good guidepost.  All use 800+ or 850+ down.  they all look good.  i'm leaning toward the MH Ghost.

Western Mountaineering Bison, 42 ounces of down, -40F

Marmot Col, 42 ounces, -20F

Valandre Odin, 42 ounces, -43F

Mountain Hardwear Ghost, 42 ounces, -40F

Feathered Friends Snow Goose, 44 ounces, -40F

North Face Inferno, 47 ounces, -40F

Marmot CWM, 48 ounces, -40F

Valandre Thor, 50 ounces, -50F

Feathered Friends Snowy Owl, 51 ounces, -60F

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