- Mar 25, 2015 at 10:08 am #1327239Niek van GriethuysenBPL Member
I am trying to find out what the best way is to keep your down sleeping bag dry in freezing temperatures. There are a lot of threads on this subject, but none comparing different methods.
Picture a week long trekking on snow and ice, temperatures at night would be between -10 to -20 degree celcius. Sleeping would be done inside a double wall tent. No drying your bag during the day (to cold).
The question is: how to deal with condensation of sweat? In a normal down bag, you would wake up in the morning with ice covering your sleeping bag. When packing the bag to move on, ice will be packed with the bag, maybe melt during the day, get through the fabric and whet out the down. Not to speak of water that has condensed inside the bag.. As I see it there are a couple of options:
1. WPB outer fabric on sleeping bag
2. WPB bivy
3. Breatable uncoated nylon lightweigh bivy bag
4. vapor barrier inside bag
5. synthetic insulation overbag
6. Creating lots of ventilation in your tent
As I have already read some post on this subject, I believe option 1 is no good. WPB outer would keep more condensation inside the bag. Same for option 2. Option 4 sounds to me like a very uncomfortable solution. (I have once slept in a non-breathable bivy and woke up in the middle of the night in a pool of sweat.) Option 6 I think won't work, since the frost build-up on your bag would also happen when sleeping outside(correct me if im wrong).
Is it possible to keep a sleeping bag dry over multiple nights. I would love to hear all your experiences and ideas. Thanks.
NiekMar 25, 2015 at 10:26 am #2185883James CahillBPL Member
@dmatbLocale: Norf Carl
While there are others here with much more experience and hopefully they chime in, all I can suggest is don't give up on the VBL too quick. Waking up in a pool of sweat sounds like you were too warm. A VBL may work better for you if you sleep "comfortably cold" by appropriately venting so that you don't overheat and sweat yourself outMar 25, 2015 at 10:41 am #2185892
Just below freezing is way too warm for a VBL.
It depends on where you are – in the Sierra you can put out your bag in the sun and watch moisture rise off the lining, even in the middle of a snowy winter. It can be 30f at night and 80f during the day in summer.
I never worry about it even with plain old down. i have not had any problems with losing so much loft that the quilt failed to perform.Mar 25, 2015 at 10:48 am #2185896Todd TBPL Member
@texasbbLocale: Pacific Northwest
If it really is too cold to dry anything out during the day, I think the laws of physics limit you to the VBL solution–if you can't take water out, you've got to not put water in.
If you're pooling sweat, maybe you've got too much insulation and need to either take less bag or vent yourself better.Mar 25, 2015 at 11:37 am #2185919Edward BartonBPL Member
A backpackable wood stove is another option, typically used with a floorless pyramid or tipi type shelter. You can theoretically dry your bag and clothing with the dry heat it provides, though I'm not yet experienced with how well this works in practice. I will be trying it out next season. My small Wifi stove from Tigoat weighs 27oz with a 6.5ft pipe.
The breathable bivy and synthetic overbag are also good options. Both will likely move the dew point outside the down bag, though perhaps the overbag more reliably. A summer weight bag with 2.5oz Apex would probably do the trick, and is fairly easily made. I believe it also adds 10-15 degrees of warmth.
An insulated snow cave or trench can also move the dew point away from the bag, but tends to increase the humidity of the air as well.
I wonder if a snow trench may be an optimal solution, because the insulation of the snow would help move the dew point away from the bag, but the open ceiling would then vent that vapor, helping to pull more vapor from the bag. A tarp over the top of the trench could be used in inclement weather, preserving some air flow.
This is all speculation mind you…I only recently got a winter set-up together, so, next year for me…Mar 25, 2015 at 11:42 am #2185922Bob GrossBPL Member
@b-g-2-2Locale: Silicon Valley
I know that this seems counter-intuitive, but you need to make the inside of your tent better ventilated. I know it will be cold, but that air movement will carry off a lot of the excess moisture that leaves the sleeping bag. Therefore, your sleeping bag stays somewhat drier. Ultimately, that leaves you warmer while you are in the bag. However, it leaves you colder when you are out of the bag and sitting in the tent.
Also, it helps if you have the warmth rating of the sleeping bag to be correct for the temperature that it will be in. For example, if I expect the cold temperature of 0 F, then I take a sleeping bag rated for -10 F. I would not take one rated for -40 F.
–B.G.–Mar 25, 2015 at 11:43 am #2185923Stephen MBPL Member
@stephen-mLocale: Way up North
A stove would be nice, but an issue if there is no fuel due to heavy snowfall.
I do think an overquilt is a good option.Mar 25, 2015 at 6:06 pm #2186059Peter NashBPL Member
@nash-pcomcast-netLocale: West Michigan
Use a VBL. The physics are inexorable. As Todd noted above,"If it really is too cold to dry anything out during the day, I think the laws of physics limit you to the VBL solution–if you can't take water out, you've got to not put water in." Stephenson's Warmlite makes only VBL sleeping bags. Their website discusses the benefits of VBLs.
VBLs keep you warmer and protect your insulation. And contrary to conventional wisdom, they work at any temperature. I use a VBL in the middle of summer at 600 feet elevation, with temps plunging to the upper 50s. Yes, I get a little condensation around my feet. No problem really. I wipe the condensation out.Mar 25, 2015 at 7:02 pm #2186089owareusa.comBPL Member
@bivysack-com-2-2Locale: East Washington
I use pretty much all the stuff you mentioned.
I like to add more heat, hot water bottles, force more moisture out of the bag.Mar 25, 2015 at 8:33 pm #2186130Franco DarioliBPL Member
@francoLocale: Gauche, CU.
I have only slept in temps of around 20f and up , at those my take is that ventilation does help a lot.
Last winter on two consecutive almost identical nights , on the same spot, I had a rather damp first night (wet under fly and collapsed sb foot box) because by mistake I had my top and bottom vents closed, the second night both were open resulting in a dry bag and dry fly in the morning.
BTW, having had a good look around in the morning, the other tents that were all sealed up (we were on snow ) were wet in the morning, later to have folk drying their bags in the sun.Mar 26, 2015 at 12:16 am #2186179Anonymous
If you're spending $ and weight on bivies and VBLs why not just switch to a synthetic insulation bag? Several of my cold weather backpacking friends seem to prefer synthetic for that reason.
Unless you're below 0 F, go ahead and change your clothes including underwear and socks. clothes can bring a fair amount of moisture into the bag.
Make sure you don't breathe inside the bag. Drape a scarf/shirt over your nose to keep it from freezing but don't tuck the scarf in into the bag. That way the scarf won't pull moisture into the bag.
If you're sweating, unzip the bag and move a leg in/out to regulate temp.
Hanging your bag before and after bed will probably help dry it more than you think. Cold air can be extremely dry, helps evaporate out that moisture.Mar 26, 2015 at 12:55 am #2186181James holdenBPL Member
these are time problem methods used by folks in the moutains/polar regions
also note that even if its cold the sun can help dry the bag … a dark colored bag helps this process
;)Mar 26, 2015 at 4:40 am #2186192Don SeleskySpectator
Another vote for some kind of VBL. You can use a VBL bag inside the sleeping bag, but that would mean that the moisture would be retained in any clothing you'd be wearing. That would not be good if you wear any down clothing to bed. Instead, try a VBL shirt and cap over your base layer. Various companies make them, such as RBH Designs and Stevenson's Warmlite.Mar 26, 2015 at 6:34 am #2186217
If you are sweating, take off a layer, do something to not sweat. If it's just the normal moisture that always comes from healthy skin, it can be managed with ventilation of the shelter.Mar 26, 2015 at 7:02 am #2186235Niek van GriethuysenBPL Member
Thanks for all your responses!
Most people would prefer a VBL. After reading all your experiences and opinions I agree. Looking at the phisics this would be the only real solution.
A synthetic bag would I think have the same problem, it is just not affected as much by water as a down bag. A stove would be nice, but heavy and would require some extra skills.
A very good point by James was made, to have a sleeping bag that is a bit to cold for the situation. When you are not to worm, you sweat less, so less of a problem. You would be able to add wormth by adding layers.
Drying your sleeping bag in the sun is worth the efford, even in very cold condition.
Sleeping bag should always be with a non-waterproof shell. So just a lightweight nylon with dwr.
When sleeping in -10 degree C (14 degree F) or colder: Use a VBL
When sleeping in -10 to 0 degree C (14 to 32 degree F): Use a lightweight nylon overbag. Since the dewpoint in these temperatures is outside the bag, all you need is a layer to keep the water from you sleepingbag shell.
In -5 degree C (23 degree F) and up: you don't need an extra layer, provinding you have enough ventilation.
Have we now come up with the ultimate conclusion that answers dozens of forum threads? :-pMar 26, 2015 at 7:09 am #2186239
I don't use a VBL because I've never needed one.
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