-40 deg F sleeping bag selection

4:59 p.m. on February 14, 2013 (EST)
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Hi,  I am conducting fieldwork in the Brooks Range in Alaska in late April and am a poor geology graduate student and do not want to foot a bill for a down -40F sleeping bag.  Do people think that the synthetic TNF Dark Star will cut it?  Or, is there a place that will do air mail rentals of -40F bags in the US besides EMS or REI (often they do not carry such warm sleeping bags).

Any input would be appreciated! Thanks!

7:11 p.m. on February 14, 2013 (EST)
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Well... that's a difficult question and depends upon:

1. Where you will use it. (cabin or tent or snow cave?)

2. Moisture buildup from use (How often can you totally dry it?)

3. Your fittness level (Very fit people have a high metabolic rate and tend to sleep warmer.)

4. Mattress(es) (Does it give adequate insulation?

5. Head cover (will your also wear a warm balaclava and face cover?)

And I'm sure there are other variables such as how soon before bed was your last meal and did it contain sufficient complex carbs to fuel your body all night. Also staying properly hydrated plays a big role in staying warm.

Personally I would try to use VBL clothing over a pair of light polyester long johns or a VBL inner bag to keep the main bag dry. Also, on brutally cold nights your can wear down or synthetic jacket and pants to bed. This setup (Thermolite Micro insulated pants & jacket)  allowed me to take a 30 F. WM down bag to 15 F. comfortably in a Tarptent Moment with 35 to 45 mph winds gusting all night.

Seriously consider the VBL pants and jacket because it also can be used in the daytime to keep insulating clothing dry in anything below 0 F. Again, lightr poly long johns next to your skin keeps your from feeling clammy as sweat builds up beneath the VBL suit.

** You may decide against VBL for clothing or sleeping but you should DEFINITELY use a pair of VBL socks over thin poly sock liners. My very favorite VBL sox are thin neoprene foam diver's sox that I have seam sealed. This setup keeps your boot feltpac liners or other insulation from getting wet and cold.

7:14 p.m. on February 14, 2013 (EST)
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i used the dark star for a number of years; my review is posted on trailspace.  though it said -40, i thought it was more like -20 to -25.  keep in mind that i sleep 'warm,' i don't easily get chilled.  i used it on nights that were -20 and -25 with a very thin bag liner (cocoon, i think) and was fine, but i was glad it didn't get much colder.  it may be perfectly fine for your purposes.  

you could try geartrade.com or ebay.  i just looked at both and saw a marmot col (-20f down bag) on each site, both selling for prices between 325 and 350.  that is about the same price as a full retail dark star.   

by the way, i saw the comments about VBL (vapor barrier liners) and sleep pads.  you definitely need to think about the R value of your sleep pads to ensure you are insulated from the cold ground.  a too-small buffer between you and cold ground means  you won't be as warm, regardless of what sleeping bag you use.  i use two closed cell foam pads in -20 or colder; a lot of people combine one closed cell foam pad and one inflatable pad, like a thermarest.  REI's website may have an R value calculator that helps explain how much sleeping pad you might want.  

a vapor barrier liner for a sleeping bag is a coated nylon bag liner that prevents all moisture from evaporating away.  vapor barriers can be really helpful in cold weather sleep situations.  without a vapor barrier, moisture evaporates from your body naturally while you sleep, it enters the sleeping bag's insulation and pushes toward the outside.  on really cold nights, though, the water vapor might not evaporate away from the bag; it can freeze within the outer edge of the sleeping bag's insulation and eventually compromise the loft of the bag if you don't have the opportunity to air the bag out.  

sleeping with a vapor barrier liner is an acquired taste - some find it pretty damp/uncomfortable.  effectively, it's like sleeping inside a plastic dry-cleaning bag.  you virtually must wear long sleeve wicking layers and socks.  it does effectively add some warmth, and it does protect the loft of your bag.  they are inexpensive, too.  a vapor barrier bag liner costs only 25-27 bucks at campmor.  

10:14 p.m. on February 14, 2013 (EST)
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I use a tyvek suit as a vb, I pay four bucks for them at an overstock store. I do wear long wicking clothes under it. I can extend my bag by 20 degrees with this system, I also use a sts thermolite reactor, and a bivy on the outside if I need it. I am a very warm sleeper, ive slept soundly at -5 with a 20 bag many times at -10 I wake up cold.

10:52 p.m. on February 14, 2013 (EST)
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A big question I have is what is the fill in the Dark Star? I'm thinking Climasheild but I am not going to bank my money on this being the case.

I have a Tundra-20 and while this bag has received questionable reviews with the Polarguard & Climasheild fill my bag has Primaloft Infinity(continuous filament) fill and I have had no trouble of ever being cold in this bag.

Just keep in mind what is under you in cold temps is just as important as what is around you.

You could have the warmest bag on the planet and freeze your tail off if ya don't have something between you and the cold ground.

12:11 a.m. on February 15, 2013 (EST)
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Is -40 your number, or theirs?

If you need to be protected to -40, I would not count on a Dark Star to get me there. Then again, I've never used a North Face sleeping bag; I'm basing my assessment on what I've commonly seen with synthetic bags in general, in that they are often rated quite generously...the only line I've heard of that stacks up is the Mountain Hardwear Ultralamina series.

I'd look for an older Marmot CWM on Ebay or Geartrade. You should able to find one for under $250.

12:33 a.m. on February 15, 2013 (EST)
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One important question? Are you hiking in to your designated area? If a supply depot or vehicle is close, consider two bags. One inside the other. Much cheaper but heavier. You already know the speech on ground insulation and sleep clothing. I would think that a 0 degree bad with a 20 degree bag would do the trick. Basically looking for 10" of loft total, that should do the trick.

8:58 a.m. on February 15, 2013 (EST)
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Thanks for the all the advice so far! I will definitely check out geartrade or ebay.  We are driving up the haul road from Fairbanks to Coldfoot, then flying to our field site in the Brooks Range via float plane (ski plane in winter?).  I won't be doing any hiking or much physical labor except what's involved with drilling sediment cores out of a frozen lake. I'm only 5'6", so I'm thinking I could put my shorter women's specific summer bag into a longer used Marmot CWM or similar.

1:29 p.m. on February 15, 2013 (EST)
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For below zero temps on a trip supported by helicopters or pack animals I always bring multiple sleeping bags and blankets.  They can be used in different combinations and air-dried more easily to remove moisture and ice that form over time.

1:45 p.m. on February 15, 2013 (EST)
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In that case, Liz, layer away! I wouldn't necessarily get a deep winter bag then...As Schlock says, a 0 degree and your current summer (20 degree? 30 degree?) bag should get you there as long as they combine for either around 10" of loft, or 45 ounces of down, total...

4:54 p.m. on February 15, 2013 (EST)
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My advise, for what it's worth. If I were flying over the Brooks Range in a bush plane in the winter I would have the warmest sleeping bag I could find. The Marmot CWM should be good all on its own.

In my part of the Canadian Arctic you can no longer board a plane without adequate gear.

11:12 p.m. on February 15, 2013 (EST)
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My own solution to ultra cold temps has been a Mt'n. Hardware -20 F. Polarguard Delta bag that has a zippered 6" wide expansion gore parallel to the main zipper.

When this expansion gore is unzipped there is plenty of room inside for my WM Megalite down bag. Down inside and synthetic fill on the outside is good since most of the body moisture will migrate to the synthetic fill, where it will affect the bag loft far less.


The only drawback is that the Mt'n. Hardware -20 bag is SO big that I have to strap it on the bottom of my Dana Designs Terraplane pack in its own compression sack B/C it won't fit in the pack's "sleeping bag compartment". Plus that sucker is heavy.



5:18 p.m. on February 16, 2013 (EST)
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The place to ask about this is on www.wintertrekking.com The members there have a lot of experience in very cold weather. Most of them are in Canada. Here is a link to the wintertrekking article on bags-


Here is a forum thread on choosing a bag-


If you are really going to be out in -40F, I would say you need a -40 bag. Out in the field is no place to find out your bag isn't warm enough. I think a VBL may help, but I've never used one, just based on what I have read from those who do.

A couple of inexpensive choices - US Army or CF (Canadian Forces) extreme winter bags. You see them on eBay all the time and surplus shops sell them. Each has a combination bag. Some of the folks on wintertrekking use them.

One thing I would not do is believe the ratings of a cheap bag or one made by a company I don't recognize as a high end bag maker. Their claims are often wildly optimistic to be polite about it. That narrows down the field quite a bit.

Used deep winter bags are a good way to go if you know what you are looking at. I picked up a Marmot bag in like new condition for half of retail last year. I've seen Western Mountaineering bags on Craigslist for about half retail, still not cheap, but not $700 either.

One name you will likely hear is Wiggy. He is somewhat controversial for various reasons I will skip but a Google search will give you more info on his bags. Some people love them, some don't. There is a thread here about Wiggy somewhere. Use "Search" to find it.


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