- Nov 21, 2017 at 12:42 am #3503183
You *should* be OK, with two 6″/150mm bags and your parka, but -40 is cold.Nov 21, 2017 at 6:13 am #3503236
“Generally a good sleep system for -40 or so will weigh several pounds more than an entire UL kit in summer. ”
OK I really appreciate that information as what I have assembled to try out does weigh more than my complete FSO summer kit. So my 6.5 to 8 kilos isn’t unreasonable then? Tent extra naturallyNov 21, 2017 at 6:21 am #3503238Roger CaffinModerator
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
Scott (and others) found that by the end of the voyage their ‘sleeping bag’ could weigh several times it’s original weight. The extra was ice, inside.
CheersNov 21, 2017 at 7:57 am #3503254Ryan JordanAdmin
@ryanLocale: Central Rockies
Looking back thru my notes, here’s what I used on a 45 below night in SW MT, but can’t confirm, as that was only a “reported temp” by a nearby weather station (5 miles away, similar elev.) and not an actually measured temp.
I do know it was something below 35*F — that’s where my digital thermometer at the time bottomed out.
I used this:
* WM Puma
* BPL UL Merino hoody and bottoms (no longer available, but 115 gsm merino)
* BPL Cocoon pants and hoody (no longer available, similar in warmth to Patagonia MP)
* run of the mill sort-of-wind-resistant balaclava, probably an OR brand?
* Nunatak down balaclava and booties.
* MLD eVent Bivy
* XTherm pad + GG Thinlight pad.
I fared pretty well, and slept good from about 11AM to 6AM. Then I scampered into a nearby cabin and slept even better for a few hours longer!!
It was windy (mildly breezy, but mild breezes get intense when it’s this cold) –
10 mph maybe? out there, but I was below the treeline and that helped.
No tent.Nov 22, 2017 at 5:06 am #3503443
Ryan was that just the bivvy or were you also inside a tent?
My current winter bag is somewhere between the WM Apache and the WM Badger in spec to give you an idea of what I am using.Nov 22, 2017 at 1:44 pm #3503469
Note that Ryan was not using a tent.
Note his body layers.
Note the Bivy
Note his balaclava’s.
Note his ground insulation. (Likely a bit weak, I would be looking at an R7 for starters…but snow can be a good insulator,)
Note that he woke up and went inside…Be prepared for -50F in Alaska…
Like I said, you want about 11″ of loft in a good bag (with lots of features. For example: one regular Apache and one xwide/xlong Badger to avoid too much compression.) Also a good, breathable bivy, At those temps, a vapour barrier makes sense for multi-night trips.Nov 22, 2017 at 6:30 pm #3503521Ryan JordanAdmin
@ryanLocale: Central Rockies
Confirmed: no tent.
“I fared well” = it was not a toasty, comfortable night where I woke up feeling well rested. Remember, I scampered into the cabin before dawn!Nov 22, 2017 at 7:43 pm #3503535Jay CableBPL Member
I have slept a handful of times outside at ~40 weather, some of those times in pretty remote places. The last few years I have biked the iditarod trail in alaska during the dog race.
I use a -40 rated down marmot bag. I am doing it again this year.
A couple of things to think about –
Moisture – after about 4 days or so my sleeping bag starts to get a bit colder, due to the moisture. If you are not going to have a chance to dry out your gear inside and are going to be out longer than that, I think a vapor barrier (or possibly a synthetic bag) would be a really good idea.
Room – at those temperatures, anything you want to keep warm (unfrozen) needs to go in your sleeping bag. I normally keep a water bladder, and a few extras inside the bag with me, but you might also want to keep your boots inside the bag too. So I would make sure you have a bit of wiggle room in the bag.
Hood/bag opening – perhaps this is obvious, but you will want to synch down the opening on your bag as small as possible, so you lose as little heat as possible, yet still can breath and down vent moisture into your bag.
If you are using a tent, I wouldn’t use a bivy, they just trap moisture. If you are not using a tent, I would bring a bivy, but not use it unless it is near freezing.
If it was me, I wouldn’t screw around with using two bags, and would just get one bag rated 10/20 degrees above the coldest temperature you expect you might sleep in. Maybe adjust that down if you plan to sleep a lot.
Bags are not that expensive in the scheme of things and given the cost of traveling to Alaska. I think you can rent them too in a few places in Anchorage.
How are you planning on traveling? On ski? On foot/snowshoe? f
Best of luck with your adventure!Nov 22, 2017 at 8:27 pm #3503543
I’m retired so my time is my own and my visa will be for 90 days
I have no concrete plans as yet
Have I mentioned that my parka is rated -30C for sleeping? Richard Nisley gave it a -70 rating for active use.
Thanx YES I have taken note of all the information and experience on this forum; especially about ground insulation and shelter from the wind
If I need a Snowy Owl and can rent one that would be OK too but if I’m there for 90 days buying should normally be cheaperNov 24, 2017 at 5:36 am #3503776
One thing I am having trouble with is these warmth calculations for doubling up.
If 3 inches of insulation is needed at 0F and FF give a -60F rating to a Snowy Owl with 6 inches of insulation why does the BPL formula only rate the combined insulation of 2 bags that total 6inches only -35F?
I know the US army and the US Antarctic division use 4.5 inches for -60F but I prefer the more conservative figuresNov 24, 2017 at 2:42 pm #3503811
Usually, bags are rated by adding both sides together for loft. So, when I say 11″, that is only 5.5″ per side.
As I said, the BPL “formula” starts breaking down around 0F. While temperature ratings are not linear in overall perception, the formula *is* linear. Remember that there are two kinds of heat. The first is the shaking of molecules. The second is IR radiation. IR is actually exponential in regards to the distance from the source. Most will approximate large bodies to a center point rather than go through the longer calculus for the full range of frequencies. Anyway, without including this component, numbers can skew when only approximated…in this case comparing a linear and exponential type curve. Good enough for rule of thumb, but not at the extreme ends. -43 degrees is extreme. Basically the difference says there are other factors for Rvalues of sleeping bags. Your personal Perception of Heat is important. And Winds. And Moisture. And Shelter. Follow?
An example: 6-8″ of insulation in the side wall of a house is fine. On the graph between cost of insulation and Rvalue this is a good insulation. Why don’t we use 10″ or 12″? From an economic standpoint, it costs much more to use these that what you gain in energy loss, *not* because the 12″ isn’t a better insulator. In this case, economics is driving this. There are a LOT of factors driving what Rvalue is needed anywhere.Nov 24, 2017 at 2:52 pm #3503813Jerry AdamsBPL Member
@retiredjerryLocale: Oregon and Washington
“Scott (and others) found that by the end of the voyage their ‘sleeping bag’ could weigh several times it’s original weight. The extra was ice, inside.”
wear a vapor barrier next to your skin, or maybe a base layer underneath, if you’re going to spend many nights when it’s really cold
stephenson warmlite has some good info. Their sleeping bags have a vapor barrier liner, but maybe it’s better to wear a vapor barrier, then have some of your insulated clothing over that.Nov 24, 2017 at 3:09 pm #3503815Jerry AdamsBPL Member
@retiredjerryLocale: Oregon and Washington
“One thing I am having trouble with is these warmth calculations for doubling up.”
For example, if a sleeping bag is inside a 2nd sleeping bag, and there isn’t enough room so the 1st bag is compressed, it won’t work very good. It depends how much compression there is.
Theoretically, if one bag is good to 32 F, that’s a 60 F drop from your skin temperature of 92 F. If another is good to 42 F, that’s a 50 F drop, so together they’d provide 110 F drop or -18 F.
But the surface area of the outer bag will be larger so there will be more heat loss. If your torso is 42″ around, and you have a 3″ loft bag, it’s outer circumference will be about 20″ bigger so there will be about 50% more heat loss, so lower temperature drop across the outer sleeping bag.
Plus compression. Maybe that BPL formula (or whatever) is an approximation that will get close.Nov 24, 2017 at 4:24 pm #3503827
I always use half the loft, my current bag has 155mm of loft in the torso and 140 in the legs, one of the reasons it is going in to be cleaned and topped up
I know that loft is only part of the equation and that there are benefits to overstuffing
Good point about radiation heat loss and surface area but how big a factor is that when talking about 150mm of insulation? Also isn’t this one of the other reasons for choosing black as the inner colour?
My legs do not sweat much so while I have a VB shirt I may have to make VB pants or a VB half bag but I still need to do some experimenting with the SOL reflective semi-breathable bivvy used as a liner over our Southern winter
The SOL bivvy fits inside my bag easily, the bag is about 20mm wider than the bivvy, I thought that this might help with some internally forced compression issuesNov 24, 2017 at 5:56 pm #3503869
I just find it easier to simply lay out a bag then eyeball the top for a down measurement. It is easy enough to split this in half, so easy I don’t really think about it. I believe WM does the same. FF doesn’t list loft, but I am sure their cold weather bags are quite warm enough. They use a differential fill for top/bottom, assuming you will be sleeping on snow…a pretty good insulator.
One of the nice things about the Klymit Xframe was the larger holes allowed any down beneath you to be used more or less. These were definitely warmer than a NeoAir, but you still need three pieces. Neoair, CCF pad, Klymit inside your bag. The Exped R7 pads are really good for cold weather. Saves didling with lots of pieces with snow-sleeping gear.
As far as vapour barriers go, you can make a simple one out of a couple emergency blankets and some duct tape. But, be aware that if you are using any down clothing in your bag, they will get a bit wet. (Not really as important with merino wool/fleece combinations.) When I was out in winter, I avoided VB’s because I didn’t like the clammy/wet. When you wake up, and, try to get out with minimal clothing, I froze. But I usually was only out for two or three nights at around -25F in the ADKs many years ago. I don’t go out in winter, anymore.Nov 24, 2017 at 7:59 pm #3503884Roger CaffinModerator
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
IR is actually exponential in regards to the distance from the source.
Just for the record, it’s actually quadratic. The night sky can be damn cold too down to -70 C I think.
CheersNov 24, 2017 at 11:37 pm #3503923
Well, anything with an exponent has a the same order, Roger. Doesn’t mater much how fast it goes up, they all look alike when graphed. I was referring to the “Big O” or order of magnitude.
Yeah, when you consider molecular movement, the atoms move very fast, hence on one scale “space” seems hot. Yet because of the density, it is actually very cold on another scale. Weird…Nov 25, 2017 at 2:49 am #3503960
I just checked the FF website, although I did only check the description for the warmest bag and they do say 300mm of loft
I’m headed up to Melbourne on Monday to check out a locally made SB that may just be big enough to use as an outer layer but it has a side zipper and I really do dislike zips on the side, still if it fits it is $450- dollars cheaper than the Nunatak custom bag and $450- seems a lot of money to have the zipper in the right placeNov 25, 2017 at 11:29 am #3503989
http://featheredfriends.com/snowy-owl-expedition-down-sleeping-bag.html No loft is given. Which web site are you looking at? Anyway, ~12″ or 300mm about jives with -60 or so. I tend to take loft in many bags less seriously, because there is a lot of “gaming” going on. One of the things they do during down testing is overwash the down being tested. Then use air injection to completely open every cluster. And so on. Weight for anything less than a 32F/0C down bag is the more important number. Here is a link to the Snowy Owl I looked at, for example: http://featheredfriends.com/snowy-owl-expedition-down-sleeping-bag.html Many governments are getting fussy about the internet.
As I say, loft is only about half of the warmth of a bag and is a rough measurement.
Anytime you spend that much, you are damn correct. You should get what you want!!
Edited to include the specs here.
<table id=”product-attribute-specs-table” class=”data-table”>
<tr class=”first odd”>
<td class=”data last”>Reg 6′ 0″ / 183 cm | Long 6′ 6″ / 198 cm</td>
<td class=”data last”>64″ / 60″ / 39″</td>
<th class=”label”>Fill Power</th>
<td class=”data last”>900+ Goose Down</td>
<th class=”label”>Fill Weight</th>
<td class=”data last”>Reg 52.9 oz / 1,501 g
Long 55.7 oz / 1,580 g</td>
<th class=”label”>Lining Fabric</th>
<td class=”data last”>Pertex® 30 denier nylon taffeta</td>
<th class=”label”>Country of Origin</th>
<td class=”data last”>Manufactured in the USA from imported materials</td>
<th class=”label”>Packed Size</th>
<td class=”data last”>9″ x 21″ | 35L</td>
<th class=”label”>Average Weight</th>
<td class=”data last”>Reg 5 lb 0 oz / 2,273 g
Long 5 lb 4 oz / 2,403 g</td>
<th class=”label”>Sleeping Bag Shell Fabric</th>
<td class=”data last”>Pertex® Shield EX waterproof/breathable</td>
<th class=”label”>Temperature Rating</th>
<td class=”data last”>-60ºF / -51.1ºC</td>
<tr class=”last odd”>
<th class=”label”>Zip Side</th>
<td class=”data last”>Left</td>
Nov 27, 2017 at 5:58 am #3504278
I got the 12 inch/300mm loft figures from reviews over at Trailspace
I just got back from the factory showroom where I dropped of my old bag for a top-up and rejuvenation and tried combining sleeping bags
Combining my bag filled with the lowest FP down inside an outer rated to -11C gave a free loft of 320mm
I’ll have the factory overfill the outer by 10% or even 15% but -11C is usually considered enough for Australia given the room inside these to wear extra clothing at need
The total weight penalty over getting a Snowy Owl is about 190 grams but I save over $1100- AUD and my combination is about 20mm bigger inside
I have extrapolated weights to account for the overfilling using 800FP downNov 27, 2017 at 1:07 pm #3504310
Sounds like a plan. Insure you are otherwise prepared for cold weather: plenty of fuel, plenty of warm cloths, etc. Have Fun!Nov 28, 2017 at 12:57 am #3504397
I plan to take the Goretex bivvy but only use it as a back-up if something disastrous happens to the tent or if it gets wet and too warm for the double bag system perhapsDec 30, 2017 at 10:17 pm #3510029
Now I am a little bit more confused again when I thought I had things all planned out.
My mate who has done a semi-traverse of the Brooks Range in winter is advising me to use a synthetic outer bag and not a down one if I plan to use my clothing to sleep in.
His system was a third clothing a third sleeping bag and a third a synthetic overbag. This I understand quite well but a synthetic overbag rated to -15C is going to be bulky and heavy.
I have just posted in the MYOG section on a possible synthetic overbag but basically how much clothing would need to be worn in a -18C bag with a 0C overbag to be comfortably warm at -40C?Dec 31, 2017 at 12:44 am #3510056Richard NisleyBPL Member
@richard295Locale: San Francisco Bay Area
If your sleeping pad is >= R5 and your bag and over bag are correctly rated. you could sleep without supplemental clothes and still be >thermo neutral at -40C. Moisture degradation or improper fit impacts that assessment but could be compensated for by adding your existing clothes.
Simple estimation used:
-18C bag = 37.6 oz of 800 fill equiv
0C over-bag = 26.8 oz of 800 fill equiv
Total = 64.4 oz of 800 fill equiv
-36C (lower limit of my data) requires 46.9 oz of 800 fill equiv for “Male Lower Limit Comfort”Dec 31, 2017 at 2:49 am #3510093
Many thanks for that Richard
There is a fairly big difference between the makers eyeball estimate of warmth based on loft and your estimate based on fill weight.
The fill weight of the rejuvenated bag is just on 800 grams [ only 28 ounces] to give a free loft of ~150mm. I have to assume that OP are using the US army tables and not the more conservative estimates of temperature Vs loft used by Western Mountaineering in which case the bag is only going to rate -10C and that is a big difference even if it is only an inch of loft or 13mm of insulation
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