Taking a -20 F. down bag to -40 F?

Gotta add that I have a chance to camp in Montana’s Rockies this winter and temps could easily go to -40 F. (<span style=”text-decoration: underline;”>And/or North Dakota as well</span>. I’ll pick my poison soon.)

I posted this question here B/C I thought more folks would see it than in the Winter Hiking forum.

never been to -40 but something that came to mind is :
could you walk around (at camp/no loads or other exertion) at -40 with just the clothing you plan to have on inside that bag ?
If not, probably not.
(but it is a guess….)

This is basically the same question I asked a while ago

General consensus is that it works if your sleeping bag is big enough to not have the loft of either layer compromised by compression.

Franco has a valid point too that was also raised when I asked the same question.

My bag was only a -18C/0F bag

Franco,

I have experienced -40 F. (same as -40 C. – it’s where the two scales meet) as a Nordic Ski Patroller in Lake Placid, NY in 1979 on the last day of the World Cup Nordic Championships. Needless to say all races were cancelled. Spit and it would freeze in mid-air. Any unprotected skin got frostbitten rapidly, etc. etc. Very dangerous weather. It was -50 F. in nearby Keene Valley that day.

But no, I would need at least a warm hat and a shell over the puffy tops and bottoms and another down vest beneath the puffy jacket to just walk outside for, say very fast a midnight pee. Pee bottles are “de rigueur” for this weather.

I’m thinking that with my one person TT Moment DW (ripstop inner) I’d be hopefully at -30 F. inside the tent on a -40 F. night. These are temps in which tent zippers may literally freeze up from body vapor inside the tent. Pre-treatment with silicon zipper lube is required if you are at all experienced in sub-zero tenting.

But I WILL be using a VBL in my bag so my respiration will be the main culprit for “tent frost”. The outer side of my inner tent has been DWR treated and that may help shed tent frost when I pack up.

Yes, I’ll have a stove-heated wall tent to retreat into but I want to test all my winter gear on this trip.

Something I tell foreign guests (e.g. an au pair from Peru who’d never seen snow, or someone from Thailand): It can be -40 here.  -40 is 30C below -10C (a very cold food freezer) just as that freezer is 30C below room temperature (20C).  And, yes, it really is that much colder.  So imagine living your life inside that freezer – eating, hiking, making camp, and know that it is TWICE that cold at -40.

Having been in -40 a few times and -44 once, I found my fun meter bottoms out at -15F.  So my plan, should -40 happen while on a trip, would be (1) stay alive and (2) get out.  My doctor described an Iditarod that got to -50F.  The mushers were mushing to keep warm until they were falling asleep on the sled, then camping in their -40 gear until they were too cold to sleep, and repeating that cycle until the cold snap lifted.

There’s also the rule of thumb we learned in Arctic Engineering: productivity drops 1% for every degree F below 60F.  At 30F, productivity has dropped 30% to 70%.  Every dang activity – drilling a well, completing paperwork, eating lunch, setting up a tent, takes longer in heavy clothing, in gloved hands, and when you spend much of your time just staying warm.  By -40, yeah, nothing is getting done other than (hopefully) staying alive.

But back to Eric’s question:  If the extra clothing you propose adds 20F of comfort to a warmer sleeping bag, yes, I’d expect it would enable you to use a -20F bag in -40 conditions.  Assuming there is enough volume inside the -20F bag to not overly compress those clothes or the bag itself.

I like the proposed sleeping pad (which is R-4) plus the Ridgerest.  Maybe include a few straps to keep them from sliding apart.

Somebody once offered a breathing apparatus for extreme skiers with a snorkel-like mouthpiece connected to a porous layer of material on one’s chest.  The idea was, after an avalanche, instead of a a few square inches of mouth/nose to breath through, you’d have a square foot of intake which could enable you to keep breathing and give rescuers another 10-30 minutes to find you.  I’ve pondered a different idea in which a tube-in-tube snorkel with check-valves would pre-warm outside air and exhaust humidity in your breath outside the sleeping bag and tent.  Maybe even with a air-blocking but water-wicking material so incoming air was humidified too.

Also, consider that while wood, nylon and HDPE are all fine at -40, metal alloys might not be.  A pot, pack frame or tent stake that was plenty strong at 0 and -20 could, depending on its ductile/brittle point, shatter upon minor stress.  There were early Liberty Ships that sank in the North Atlantic or even upon launching.

Eric,

This thread and the graph in the OP might be useful: https://backpackinglight.com/forums/topic/9378/

The temp/clo graph doesn’t go lower than Zero F, and the slope for insulation required for sleep is steeper than the slope for insulation required for camp chores. The slope values might be down in that thread, or maybe R. Nisley can supply them for you. I suppose you could just print that chart out and extend the slopes.

I see no reason why you couldn’t take your -20 F bag to -40 F with enough clothing insulation (apart from whether your bag is voluminous enough to accommodate that insulation without compression), but having grown up in northern Minnesota, I would personally want to have it very well worked out (mathematically) before setting out in that kind of weather. I would also want to have a cushion of some sort, maybe planning for -50 and having kindling set up for a post-midnight fire, if needed.

Anyway, you’ve experience in those temps, so I’ll say no more. Except, what about your face? I remember as a kid that temps below -20 F didn’t feel that different from zero F, except for the way the snow sounded under foot and that one’s skin became numb so fast that it was easy to forget how cold it was. As you say, very dangerous.

David, I have an “avalanche breather” similar to your description. It’s called an AVALUNG . It simply takes your inhaled air from a filtered box and redirects your exhaled breath down and to one side so you do not create an icy “death mask” around your face. At best it gives and extra 45 minutes for rescuers to find and dig you out.

Stumpy, I own a now out-of-production PSOLAR cold weather breathing mask for extreme cold. It is made of fleece and covers your face chin to nose bridge. Your exhaled breath warms a layered copper screen so the cold incoming air is warmed somewhat. It does work and also keeps your noise warm. A cold nose is the bane of sleeping in frigid conditions. You are constantly, semi-consciously trying to keep it warm and that’s the main reason people’s unprotected  faces inevitably end up inside their sleeping bag, wetting it with respired vapor.

**There are similar (diaposable) cold weather masks for cardiac patients to relieve their heart from the extra work entailed when your chilled bronchial tubes and lungs require more blood to warm them.

Have you had a look at the range of down and synthetic overbags from PHD in the UK?

Ed,

Is PHD a company name?

Last time i wanted something from the UK (a RAB parka) 1. it was horribly expensive and 2. import duty was not cheap either.

But I’ll check on the overbags and see what the prices are.

Horrifically expensive but UL

Which is why I went with a local bag plus extender ///

https://www.oneplanet.com.au/product/sleeping-bags/down/cocoon/

https://www.oneplanet.com.au/product/sleeping-bags/down/expansion-gusset/

A Wiggy overbag is much cheaper but twice the weight

https://www.phdesigns.co.uk/hispar-down-overbag

https://www.phdesigns.co.uk/zeta-synthetic-primaloft-overbag

https://www.phdesigns.co.uk/thinsulate-overbag

Ed,

Thanks for those links to overbags. YIKES! the cost is eye-watering for any of them.

So I’m going to get the lightest Montbell down pants unless I can find some with a down DWR treatment elsewhere. Having experienced how well light synthetic insulated mid layer pants and jacket works in other sleeping bags down to -22 F. I think I’ll be OK with down pants and jacket.

But I may make my own overbag of Climashield insulation for my 20 F. overstuffed Western Mountaineering Megalite three season down bag to see how it works. We have a sturdy Husqvarna sewing machine that can do the job. It will be a simple tapered bag with no hood and a single layer of Climashield insulation. The lightest ripstop nylon will be fine for a shell. No zipper, just a 1/3 length Velcro closure.

Don’t skimp on the insulation. I made my overbag using a single layer of 80GSM and it wasn’t anywhere near enough and it was too heavy because of the weight of the 2 ounce Taslan shell

My custom UL overquilt from Nunatak using 100GSM also wasn’t / isn’t enough enough, great for Australia but it only adds 10C, just enough to make up for my age related drop in sleeping MET

If you can afford Robic 0.7 then using that on the foot area has benefits

Ed,

My winter sleeping protocol has me zipping up my GTX mountain parka and putting it over the foot of my sleeping bag. That parka covers about 1/4 of the bag and helps keep the foot area a bit warmer but its main purpose is to help keep tent frost from melting on the warm bag.

It just occurred to me that I do have an old duck down mummy-shaped top cover that lays over my bag up to my chin and has three elasticized straps to hold it on. I may take that as a backup.

Hee, hee  “…just enough for my age-related sleeping MET.” Well, at 74 I’ve put on enough fat to offset that drop in metabolic rate.

My first thought is no.  With a potentially less than true to temp bag I’d want more clothing.

I’ve taken a WM Antelope (5F) to -25F with a expedition down parka (12 oz of fill), 100 gram/meter synthetic pants, and fat down booties.  Comfy, but the pants were a little undergunned.  I would not have wanted less parka.

It’s all about the cut and shape of the sleeping bag.

I think that once you have dropped the sleeping temperature below -18C/0F you have moved out of UL territory simply because an Expedition cut sleeping bag needs so much fabric for the shell and more down to maintain a certain temperature rating.

In my own bag I can wear insulated pants of I can use a half bag but I can’t use both or I compromise the loft. The half bag is warmer but doesn’t have the functionality of trousers around camp. At those temperatures I want much more down in my parka than 12 ounces; luckily for me I already own one

I went the oversized / overbag route so I would have a large margin of error if it got really cold but I won’t know if I’ve made the correct decision unless I see really low temperatures; that is -55C and lower

Ed,

Your half-bag is definitely a mountaineering system, requiring your heavy down parka, which I don’t own – yet…

Yes, winter backcountry travel is definitely not UL when it comes to clothing and sleep systems. Even stoves should be a bit more robust. I use white gas (petrol) mode for my Whisperlite Universal or my Caldera Cone Sidewinder W/ Inferno insert for a gassifier stove. It’s very hot in that mode.

As for my sleeping bag, I’ve tried my -20 F. mummy with all the puffy clothes and base layer stuff and it fits well without compressing either the bag or the clothes.  My balaclava and face mask cover everything but my eyes, so no exposed skin to get frostbite. I always zip up my GTX mountain parka and put it over the foot of my bag to protect it from tent wall frost from melting on the bag and wetting it. I’m sure it also gives me a bit more warmth as well.

(Still in search of a wide-mouth collapsable pee bottle. I want to stay away from the heavy MSR version.)

A few people over at Trailspace said that as soon as they get out of their winter bag in the morning they compress it to get out as much vapor as possible so it does not freeze in the bag. Good idea, along with airing it out as much as possible. In extreme cold frost in the bag can sublimate directly into vapor.

I use a VBL from around 0F and colder, makes a huge difference… weighs almost nothing. WM’s Hotsac is great. I just wear a layer of merino inside the VBL. If I know it’s going to dip well below 0F, I take a -40 bag instead of my Antelope. That and the VBL is usually fine, but if I’m running cold I either drape a down parka over my torso under the sleeping bag, or zip it sans arms in sleeves. That cold, a down vest might get zipped over the footbox, too. Kind of depends on mood. I like to play with variations. I’ve also used a Trail Pro/Ridge Rest combo around those temps, and the combo can’t touch an Exped downmat for warmth. Honestly, given the choice of taking an overquilt or a downmat, I’d take the mat every time, along with a torso-sized chunk of foam.

Yet in my query and post Richard N says that the combination of my -18C down bag plus my 0C synthetic overquilt will be adequate at -40 and no need for insulated clothing

PHD in England give a 24C boost estimate for their synthetic overbags also.

Hmmm… Seems a bit of a stretch to me to comfortably get to -40 C./F. (same temp.) with a -5 F. bag and +30 F. over bag. Doesn’t add up, even in loft thickness.

In fact even with my -20 F. down mummy bag and a 32 F. over bag I’d wonder if -40 F. would be attainable.

Eric you are old enough to remember Gerry Cunningham.

In his little DIY book he shows illustrations of his system for extreme cold and that is what Big Agnes use as the basis of their system

I am I admit heavily influenced by his systems approach to cold weather gear The main difference between an overquilt and Gerrys “Mountain Sleeper” is the full length attachment of the insulated top to the mattress pocket, it is the lack of draughts that make the Gerry style overbag more efficient than a simple quilt IMO

I know I can push my own bag down to -25C using LW insulated pants and a LW down parka plus a thermalpro jumper, going to the heavy down parka easily adds another 5 degrees so I’m thinking Richard N is correct