Feeling clammy when sleeping in cold weather

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Feeling clammy when sleeping in cold weather

Postby Huntsman247 » Fri 20 Jul, 2018 9:52 pm

I've never really noticed this before but last couple of trips I've slept in around -5 and have had to cinch up the bag around my head. I was warm... just but not hot. I'm a cold sleeper. But I woke up each time around 4.30am feeling cold and clammy needing to drape my jacket over my body and seem to feel slightly cold and rather damp till I wake up.
I've used this bag up north in Cape York as a blanket and never got sweaty from it. ???
In these past few trips I've slept in a tent and under a hootchie. Weather has also been dry and clear skies.

My sleeping setup is:
- Trek II Sea to Summit down bag
- Klymit ultralight insulated mat
- Merino baselayers
- somedays I added a fleece jacket
- down jacket stuffed at feet with other clothes

I've researched this a bit and most people say that your too hot and therefore sweat but I'm just feeling warm. Don't think this one is the culprit.
The weather recently has been well below the comfort rating of the bag which is 0. One day was -5 with 50km winds. I didn't feel cold but certainly not overly warm.

What am I doing wrong? Any ideas/suggestions?
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Re: Feeling clammy when sleeping in cold weather

Postby jdeks » Fri 20 Jul, 2018 10:40 pm

Whats the loft in your down bag like the next morning?

And what was the overnight humidity?
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Re: Feeling clammy when sleeping in cold weather

Postby Huntsman247 » Fri 20 Jul, 2018 10:57 pm

jdeks wrote:Whats the loft in your down bag like the next morning?

And what was the overnight humidity?
Good loft. It's treated down. Humidity was low. One morning the bag had ice all over it but loft was fine and felt no different to other nights when it wasn't. Although I imagine that would have stopped the bag breathing as well as it should. But then again I couldn't tell the difference in dampness.
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Re: Feeling clammy when sleeping in cold weather

Postby wayno » Sat 21 Jul, 2018 6:51 am

humidity might have been low during the day if it was warm, but with a big temp drop then humidity goes up because the air cant hold what moisture there is, hence the frost , humidity reached 100% or dew point, then the moisture from the air above descends to ground level to concentrate, so you ended up damp, esp inside the bag moisture wouldnt get out easily in those conditions need a warmer bag or sleep with more clothes.
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Re: Feeling clammy when sleeping in cold weather

Postby Orion » Sat 21 Jul, 2018 7:51 am

wayno wrote:...then the moisture from the air above descends to ground level to concentrate...

I don't think that's quite how it works. You typically get dew/frost on exposed objects because they cool faster than the air, not because of a vertical gradient in the absolute humidity.

That aside, maybe the higher relative humidity is the source of the clamminess. I'll propose a second possibility: maybe because the bag is cinched up tighter the insensible perspiration has a harder time escaping.
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Re: Feeling clammy when sleeping in cold weather

Postby jdeks » Sat 21 Jul, 2018 9:12 am

wayno wrote:humidity might have been low during the day if it was warm, but with a big temp drop then humidity goes up because the air cant hold what moisture there is,


correct so far

wayno wrote:hence the frost , humidity reached 100% or dew point, then the moisture from the air above descends to ground level to concentrate, so you ended up damp,


Not quite. When you hit 100% relative humidity, the water vapor in the air will precipitate out as droplets, but these don't "descend". In fact they're usually warmer, due to release of latent heat of vaporization, and stay floating about in the air (ie mist).

The reason you get droplets on the skin of tents, clothes, sleeping bags is because a) they radiate their heat away and end up colder and reaching dew point earlier, b) they have warmer sources of humidity inside them, driving water vapor out through them and c) they have nice 'rough' surfaces that newly formed droplets can cling to (reducing the amount of surface tension needed to stay together). If it gets cold enough, these droplets can then freeze.

Having the drops on the skin of the bag is actually a good sign - the dew point isn't being reached INSIDE the bag walls and saturating the down with condensate. But it can be a sign of a bag with inadequate insulation - all the heat is escaping too readily and leaving the surface of the bag cold enough to hit dew point.

Huntsman, I think the problem here is quite simple - your bag isn't warm enough.

As you note, it's really only meant for around 0C, and you're pushing it to -5C. You're cold sleeper too, you say. All bags tend to hold humidity, so as orion says , youre all cinched up tight, keeping perspiration in. Net result after 7 hours in the sack? A bit chilly and and a tad sweaty aka clammy.

Get a warmer bag.

(some more reading on dew points and condensation in bags if you're curious: viewtopic.php?f=15&t=28061#p353142)
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Re: Feeling clammy when sleeping in cold weather

Postby Orion » Sat 21 Jul, 2018 9:43 am

jdeks wrote:But it can be a sign of a bag with inadequate insulation - all the heat is escaping too readily and leaving the surface of the bag cold enough to hit dew point.

I'm not sure I understand this. Are you suggesting that more insulation would result in a warmer outer surface?
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Re: Feeling clammy when sleeping in cold weather

Postby wayno » Sat 21 Jul, 2018 10:33 am

on a calm night, pitch a tent under a tree, usually no condensation on the tent, pitch it in the open and you can get condensation even when someone has pitched a tent nearby under a tent and its dry, thats the moisture descending from the air above onto the tent
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Re: Feeling clammy when sleeping in cold weather

Postby Orion » Sat 21 Jul, 2018 10:49 am

wayno wrote:on a calm night, pitch a tent under a tree, usually no condensation on the tent, pitch it in the open and you can get condensation even when someone has pitched a tent nearby under a tent and its dry, thats the moisture descending from the air above onto the tent

That's the classic example that you've misinterpreted. The reason the tree keeps the tent fly free of dew is because the tree is warmer than the sky and actually heats the tent (via radiation) ever so slightly.
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Re: Feeling clammy when sleeping in cold weather

Postby Franco » Sat 21 Jul, 2018 11:35 am

Your sleeping bag and mat should be OK (just...) at -5c for a young, healthy, well fed male.
Otherwise you need to beef up both.
(note the -1c comfort rating given to it by S2S)
possibly just adding a thin solid foam mat will do the trick when wearing extra clothing .
At the same time , don't under estimate the importance of a high calorie intake in cold temps.
The fewer calories you ingest, the less heat your body can generate.
BTW, I don't see socks (yes down by the feet but warm, clean, loose socks will help) nor a hat. A warm beanie makes a huge difference.
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Re: Feeling clammy when sleeping in cold weather

Postby neilmny » Sat 21 Jul, 2018 12:10 pm

I have the Trek III in the long version and if I get clammy around the legs I open the bottom zipper.
Being the longer version my feet don't stick out or reach the bottom so all that happens is a little bit of circulation takes the clammy away.
This probably goes against all theories of keeping warm but has never resulted in having cold feet or waking up cold.
-3C is probably the coldest night I've had. I generally sleep in thermals and a pair of fresh merino socks and on an R6 rated mat.
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Re: Feeling clammy when sleeping in cold weather

Postby jdeks » Sat 21 Jul, 2018 12:16 pm

Orion wrote:
jdeks wrote:But it can be a sign of a bag with inadequate insulation - all the heat is escaping too readily and leaving the surface of the bag cold enough to hit dew point.

I'm not sure I understand this. Are you suggesting that more insulation would result in a warmer outer surface?


Possibly.

For a given 'cold' temp - A more insulative (not necessarily thicker!) bag will retain more heat, both in its interior and in the bag's insulation itself. So, yes the outer surface could be warmer, despite having a lesser rate of thermal loss.

Except usually it isn't, for a number of reasons. Firstly, warmer bags are usually thicker dimensionally, meaning you have more distance as you move away from the body to for the thermal gradient to get lower by the time you reach the shell.

Secondly, the outer shell radiates heat to the cold environment. The warmer the shell, the faster it does this. Conversely, the better the insulation, the slower it resupplies heat to the outer shell. Net result is, at a given ambient temp, an equilibrium loss rate with a colder shell. Probably.

Take away a bit of insulation, shell gets more heat from your body, stays warmer. Take away too much though, the rate of heat loss becomes so great that the themral gradient steepens and the interior insulation starts to cool too. It becomes the boundary, and the shell just becomes part of the environment at close to ambient temp.

Hence when you add vapour or reduce ambient temp to dew point, the shell is where the droplets can form if you're under insulated. This is what I think Hunstman is experiencing. Add some insulation, bag temp warms up, shell warms up, no more droplets. But then, add some more, retain more heat inside away from the shell, and you get condensation again. Add still more insulation, then make it colder, with just the right humidity, and that condensation maybe happens inside the insulation itself.

Hard to make general rules, everything depends on each other and theres so many variables, but hopefully that clears it up a bit


wayno wrote:on a calm night, pitch a tent under a tree, usually no condensation on the tent, pitch it in the open and you can get condensation even when someone has pitched a tent nearby under a tent and its dry, thats the moisture descending from the air above onto the tent



No, thats because of raidiative blocking - those covers are holding in heat the would otherwise be radiating away from the ground into space. Whack a thermometer in the open and under a tarp and you'll see what I mean.

Riddle me this -If the moisture is 'descending', why then do droplets form on the underside of said tent?? :?:
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Re: Feeling clammy when sleeping in cold weather

Postby nq111 » Sat 21 Jul, 2018 1:52 pm

Unusual that this has only been a recent pattern.

I certainly find that I heat up a great deal in the few hours after going to bed (with a belly full of food) but then much cooler around 3-4-5am. Easy to deal with by using the sleeping bag partly to start (to not get too warm) and then slowly covering up/zipping up sleeping bag over the hours of the night.

This would describe what you are experiencing if you zip up straight away and then overheat without realising it before the early morning cool down. But that this has not been an issue for you previous the last few trips doesn't support this theory. Have you changed anything in what you eat or do prior to going to sleep in your last few trips?
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Re: Feeling clammy when sleeping in cold weather

Postby Warin » Sat 21 Jul, 2018 2:26 pm

jdeks wrote:
Orion wrote:
jdeks wrote:No, thats because of raidiative blocking - those covers are holding in heat the would otherwise be radiating away from the ground into space. Whack a thermometer in the open and under a tarp and you'll see what I mean.


The night sky (outer space) is really really cold .. -270 C!
The heat energy lost between two things is directly related to the temperature difference between those two things .. you can loose a lot of heat to that night sky.

Humm around 70 watts / m squared see https://journals.assaf.org.za/jesa/arti ... 184/3572/0

.. How dose that compare to, say, a sleeping pad with R=3? Well take temp diff as 25 C (ground = 0 and you at 25 C) then Q=25/3 = 8. something..
So that is 8 watts /m squared lost compared to 70 watts / m squared .. Do I have this right ?
The tent will lose a lot more energy that the sleeping pad, no wonder double walled tents are just that little bit warmer.
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Re: Feeling clammy when sleeping in cold weather

Postby Orion » Sat 21 Jul, 2018 3:08 pm

jdeks wrote:
Orion wrote:
jdeks wrote:But it can be a sign of a bag with inadequate insulation - all the heat is escaping too readily and leaving the surface of the bag cold enough to hit dew point.

I'm not sure I understand this. Are you suggesting that more insulation would result in a warmer outer surface?


Possibly.

For a given 'cold' temp - A more insulative (not necessarily thicker!) bag will retain more heat, both in its interior and in the bag's insulation itself. So, yes the outer surface could be warmer, despite having a lesser rate of thermal loss.


So you are saying that!

A warmer shell will lose heat to the environment at a higher rate than a colder shell. You can't have both higher heat loss at the shell and "a lesser rate of thermal loss" overall -- that's a contradiction.
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Re: Feeling clammy when sleeping in cold weather

Postby Turfa » Sat 21 Jul, 2018 3:32 pm

Huntsman247 wrote:I've never really noticed this before but last couple of trips I've slept in around -5 and have had to cinch up the bag around my head. I was warm... just but not hot. I'm a cold sleeper. But I woke up each time around 4.30am feeling cold and clammy needing to drape my jacket over my body and seem to feel slightly cold and rather damp till I wake up.
I've used this bag up north in Cape York as a blanket and never got sweaty from it. ???
In these past few trips I've slept in a tent and under a hootchie. Weather has also been dry and clear skies.


Could it just be that by cinching up the bag around your head, you have trapped the moisture from your body inside the bag ??
When you use the bag as a quilt there is plenty of ventilation to let the humid air around your body escape.
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Re: Feeling clammy when sleeping in cold weather

Postby wayno » Sat 21 Jul, 2018 3:36 pm

if dew point temperature occurs inside the outer layer of the bag then you'll add to any moisture buildup, moisture won't be able to move out of the bag.
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Re: Feeling clammy when sleeping in cold weather

Postby Warin » Sat 21 Jul, 2018 4:27 pm

Orion wrote:
jdeks wrote:For a given 'cold' temp - A more insulative (not necessarily thicker!) bag will retain more heat, both in its interior and in the bag's insulation itself. So, yes the outer surface could be warmer, despite having a lesser rate of thermal loss.


So you are saying that!

A warmer shell will lose heat to the environment at a higher rate than a colder shell. You can't have both higher heat loss at the shell and "a lesser rate of thermal loss" overall -- that's a contradiction.


More insulation = less heat loss, less energy flow ..
The insulation from the outer surface of the bag to the heat sink does not change .. and the energy flow is less ..
So the temperature difference increases from the outer surface of the bag to the heat sink .. so the bags skin temperature will rise, not fall.

That different view help jdeks? Cannot reliably figure it for the heat source (inside the bag) as both insulation and heat flow change. Simpler to look from the heat sink, that way only one thing is changing.
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Re: Feeling clammy when sleeping in cold weather

Postby Neo » Sat 21 Jul, 2018 6:56 pm

So, things I've been advised and somewhat experienced...

Full bladder, better to get up and pee as the body puts it's heat to the bladder and extremities get cold.

Full bladder, body heats up as above and gets clammy.

Don't wear extra layers, use them to fill the voids in the sleeping bag. Your body heats the air space, so reduce it.
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Re: Feeling clammy when sleeping in cold weather

Postby Neo » Sat 21 Jul, 2018 7:04 pm

From experience (limited)

Less layers does work.

Comfort level of a sleeping bag is accurate. This can be boosted somewhat.

Any kind of breeze robs the warmth from a (down) sleeping bag.

Slept sub zero in a comfort +4 bag. Had a synthetic half bag inside. My lower half was clammy, inside bag was not particularly warm. Survived. Similar to the OP scenario.

I expect to get up at least once in the night to pee, espesh if I've had a hot drink in the evening.

Sleeping up high under a tarp, any moisture and air will form a little ice at that temp/elevation.
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Re: Feeling clammy when sleeping in cold weather

Postby Warin » Sat 21 Jul, 2018 8:55 pm

Neo wrote:Full bladder, better to get up and pee as the body puts it's heat to the bladder and extremities get cold.


Better to pee into a bottle .. and then use the bottle as a hot water bottle untill it cools.
This way you relieve the bladder, don't waste heat getting out of the bag cooling your body, bag and tent, and make use of the heat in your pee.
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Re: Feeling clammy when sleeping in cold weather

Postby Huntsman247 » Sat 21 Jul, 2018 9:11 pm

jdeks wrote:
Huntsman, I think the problem here is quite simple - your bag isn't warm enough.

As you note, it's really only meant for around 0C, and you're pushing it to -5C. You're cold sleeper too, you say. All bags tend to hold humidity, so as orion says , youre all cinched up tight, keeping perspiration in. Net result after 7 hours in the sack? A bit chilly and and a tad sweaty aka clammy.

Get a warmer bag.

(some more reading on dew points and condensation in bags if you're curious: viewtopic.php?f=15&t=28061#p353142)


Hmm... Ok... Trying to wrap my head around this. Wouldn't have figured that I'm getting sweaty because I'm not warm enough. I was thinking the cinching was contributing to this... But I figured that the bags are breathable enough. That's how most bags are designed to be used aren't they?
Seems that its the consensus though. Will take a look at that link later.
I have been thinking of getting the S2S spark bag and use it as a liner given the room in the trek II.

Franco wrote:Your sleeping bag and mat should be OK (just...) at -5c for a young, healthy, well fed male.
Otherwise you need to beef up both.
(note the -1c comfort rating given to it by S2S)
possibly just adding a thin solid foam mat will do the trick when wearing extra clothing .
At the same time , don't under estimate the importance of a high calorie intake in cold temps.
The fewer calories you ingest, the less heat your body can generate.
BTW, I don't see socks (yes down by the feet but warm, clean, loose socks will help) nor a hat. A warm beanie makes a huge difference.


I apologise I forgot to add socks and headwear. I did also sleep with good wool socks and a thinner merino beanie, followed by a sealskinz wp beanie over the top and a merino neck tube.
I do eat well. I generally eat 3 generous courses and generally have a good try in making my friends jealous of the food. lol.
I'm not too keen on the foam mat... I used to use them and they just dont seem to survive much bushbashing and not too much volume left in my pack.

neilmny wrote:This probably goes against all theories of keeping warm but has never resulted in having cold feet or waking up cold.
-3C is probably the coldest night I've had. I generally sleep in thermals and a pair of fresh merino socks and on an R6 rated mat.


Yeah it does. lol.
Do you use 2 mats? Haven't seen a mat above R4.4...

nq111 wrote:
Unusual that this has only been a recent pattern.

I certainly find that I heat up a great deal in the few hours after going to bed (with a belly full of food) but then much cooler around 3-4-5am. Easy to deal with by using the sleeping bag partly to start (to not get too warm) and then slowly covering up/zipping up sleeping bag over the hours of the night.

This would describe what you are experiencing if you zip up straight away and then overheat without realising it before the early morning cool down. But that this has not been an issue for you previous the last few trips doesn't support this theory. Have you changed anything in what you eat or do prior to going to sleep in your last few trips?


Yeah, I've been baffled myself. I've slept in similar temps is a yum-cha sleeping bag when I first started hiking that was nowhere near the supposed -15 rating lol. More like +5. I was certainly cold... or should I say freezing but I never got damp...
I think this is the first time I've had to fully cinch this bag though. So tending to agree that maybe that the bag is just not warm enough but I figured that with the extra clothes on and stuffed in the bag i'd be alright. Not sure if I would have been too comfy with the bag unzipped though to regulate the temp. Everything was covered in ice by 7 pm lol. Pic just before going to sleep. The white stuff is ice. As I said I was JUST warm.
Other than a new recipe or two not much done differently apart from these few times being the coldest I've slept in this bag but not by that much.

Neo wrote:Full bladder, body heats up as above and gets clammy.

Don't wear extra layers, use them to fill the voids in the sleeping bag. Your body heats the air space, so reduce it.


I generally drink a lot of liquid throughout the night but I do pee it mostly out before sleeping and I'm young enough not to need to pee during the night. :wink:
Less layers? wouldn't you be colder then?

I might have to try a warmer bag then. Hopefully, I can find the time to get out again and test this before the weather starts warming up.
Just wondering though, Just about every sleeping bag around especially those for serious sub zero come with hoods that have a cord to cinch them up. Whats the point of it being there if the moment you use it you get damp? Is the correct usage of a sleeping bag to be hot enough that you don't cinch it up?
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Re: Feeling clammy when sleeping in cold weather

Postby Huntsman247 » Sat 21 Jul, 2018 9:21 pm

Warin wrote:
Neo wrote:Full bladder, better to get up and pee as the body puts it's heat to the bladder and extremities get cold.


Better to pee into a bottle .. and then use the bottle as a hot water bottle untill it cools.
This way you relieve the bladder, don't waste heat getting out of the bag cooling your body, bag and tent, and make use of the heat in your pee.


As long as you don't recycle it further I won't judge :wink:
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Re: Feeling clammy when sleeping in cold weather

Postby Neo » Sat 21 Jul, 2018 10:29 pm

Theory there is your body heats up the bag airspace rather than the layers.
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Re: Feeling clammy when sleeping in cold weather

Postby Huntsman247 » Sat 21 Jul, 2018 10:48 pm

Neo wrote:Theory there is your body heats up the bag airspace rather than the layers.
Isn't less air space better?
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Re: Feeling clammy when sleeping in cold weather

Postby jdeks » Sat 21 Jul, 2018 11:41 pm

Orion wrote:So you are saying that!

A warmer shell will lose heat to the environment at a higher rate than a colder shell. You can't have both higher heat loss at the shell and "a lesser rate of thermal loss" overall -- that's a contradiction.


Come on, man. Don't ask a question, then misquote the answer for the sake of making a contrary rebuttal. I made exactly that point in literally the next sentence.

jdeks wrote:Except usually it isn't[/i], for a number of reasons. ...

Secondly,[b] the outer shell radiates heat to the cold environment. The warmer the shell, the faster it does this. Conversely, the better the insulation, the slower it resupplies heat to the outer shell. Net result is, at a given ambient temp, an equilibrium loss rate with a colder shell. Probably.


So yes, more insulation = colder shell and less heat loss. Unless you OVER insulate but thats another scenario...

Takehome message here is that it's an interlinked multvariable system. It's not just "more x = more y".

Warin wrote:More insulation = less heat loss, less energy flow ..
The insulation from the outer surface of the bag to the heat sink does not change .. and the energy flow is less ..
So the temperature difference increases from the outer surface of the bag to the heat sink .. so the bags skin temperature will rise, not fall.

That different view help jdeks? Cannot reliably figure it for the heat source (inside the bag) as both insulation and heat flow change. Simpler to look from the heat sink, that way only one thing is changing.


...


Okay I'm goinna lay this out in a bit more detail. Whether folk read it is up to then, but dont come back at me unless you get to the bottom.




Heat energy creeps from the body outwards through the insulation, warming it as it goes. The speed of this is pushed by temperature difference, at first between the warm body and the inner skin of the bag, then between the warming inner skin and the first 'layer' of down, then between this layer and the next, and so on, right up to the outer skin.

As the outer skin finally receives heat energy, it too will warm. But - it loses heat faster, by convection and radiation to the cooler outside. It will heat a little, but tends to find balance closer to ambient, as the skin needs very little thermal difference to drive that radiation, but the outer insultion (being, yknow, insulative) needs a greater thermal differential to match in supply what the skin loses. That outer insultion will then also itself cool somewhat, choking its own transfer, until an equilibrium is established. This cooling will creep a little back up the insulation layers, and evetually establish a thermal gradient through the bag, with a heat loss rate to the outside defined largely by the insulation.


The specific temperatures of this gradient, depend on MANY things

Now, lets drop the outer temperature. The skin sgain radiates faster than it can draw from the outer insulation at first, and its temp drops, until it reaches a new point where the thermal diffrence draws as much heat fromthe insulation as it emitts by radiation. The outer insultion also cools accordingly, and a slightly steeper temperature gradient establishes in the insualtion. More importantly, the rate of net thermal loss only drops marginally - the reduced ouside temps have in turn lowered the insulation and shell temps, in itself moderating heat transfer rates.

On the inside, you probably barely notice - interior insulation and skin temps likely stay the same. This is, roughly speaking, the comfort rating of your bag.

Now drop the temperature more. Eventually, you reach a point where then skin simply cannot suck heat fast enough from the outer insulation to replace the rampagin radiation. What gets there may warm the skin fractionally, but that just accelerates the rate it radiates out, and it cools again until it ultimately approaches ambient. The skin just keeps leechnig heat out, until the outer insultion cools enough (ie also near ambient)to lower thermal drive to the shell and reach and new steady state, as it in turn draws heat from deeper in the bag. Eventually, it self limits as the increasingly cold insulation drives less heat outwards - but just when/where this happens depends on how cold it is outside and how hot the body inside is. You could end up with the skin, and several cms of outmost insulation all at ambient temps.

You can still feel warm like - in fact this is probably where most winter hikers are at. The overall heat loss isn't much less, and if the temp gradient doesn't lower too much, the inner insulation can still be at around body temp.

However- if ambient temp is at, or close, to dew point, this is one sceario where you can get condensate on, or in, your bag, depending on humidity. And if it goes too far, you then lower the temperature of your inner insualtion and inner bag skin. You feel 'cold', and any humidity, be it perspiration or otherwise, has no heat to vaporize it and drive it though and out of the bag wall (hence feeling clammy). This is the bottom end of your comfort rating, and this is where the OP is at.


Going much colder than this, and the temp differential will drive heat loss through the full insulation thickness faster than the human body can keep up with. You're just delaying the inevitable - how long for, is how you get the 'extreme' or 'survival' rating.

So now, lets increase the insulation. Skin's still ambient-cold and thus wont get colder, but the heat isn't leaking to it as fast . Ergo, the insulation warms up - first the inner layers, but then progressively to the outer layers. Some of this leaks to the skin, whih in turn radiates away, but it's slower because the insulation is better. The insulation builds heat until a new equilibrium is reached, this time with a much warmer insulation temp, as a much larger differential is needed to drive heat into the skin at the rate it then loses it to then enviroment.

Increase the insulation even more, and you can potentially hold so much heat that the bag skin will then warm, even with the consequent increase in radiant heat loss. In this case, you will indeed be losing more heat energy, but youd want to be - or you'd probably overheat. THIS is the other 'clammy' scenario - bag is borderline too warm and you wind up sweating inside then chilling. I doubt this is the OPs problem though.
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Re: Feeling clammy when sleeping in cold weather

Postby Neo » Sat 21 Jul, 2018 11:57 pm

Huntsman247 wrote:
Neo wrote:Theory there is your body heats up the bag airspace rather than the layers.
Isn't less air space better?

Kinda a double whammy. If you are wearing lots of layers, your body/body-heat is warming those layers but not the overall cocoon of the sleeping bag. So the airspace within the bag isn't getting and trapping much heat. Wearing just a thin thermal layer, your body heat radiation warms the surrounding inner air, thus having less airspace to warm is better.

I dunno why but I have had the clammy inner but bag not so warm effect too.
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Re: Feeling clammy when sleeping in cold weather

Postby jdeks » Sat 21 Jul, 2018 11:58 pm

Huntsman247 wrote:
Hmm... Ok... Trying to wrap my head around this. Wouldn't have figured that I'm getting sweaty because I'm not warm enough. I was thinking the cinching was contributing to this... But I figured that the bags are breathable enough. That's how most bags are designed to be used aren't they?

...
Just wondering though, Just about every sleeping bag around especially those for serious sub zero come with hoods that have a cord to cinch them up. Whats the point of it being there if the moment you use it you get damp? Is the correct usage of a sleeping bag to be hot enough that you don't cinch it up?


You're not getting 'sweaty' because you're cold. You're constantly perspiring and emitting water vapor, you're in a cold alpine environment with high relative humidity, and your bag is too cold to keep your sleep zone warm enough to keep your perspiration as vapor. Bags, jackets and everything else is only breathable if the water is evaporated. When the whole bag, and well as you and your pants, are under dew point, that goes out the tent door.. Hence it's gathering as 'clammy' condensate on you and the inside of your bag.

Go try it somewhere REAL cold like Majura, and you'll get to wake up with the wonderful experience of having your own clothes frozen to the inside of your bag., while you're still wearing them.


Cinching the bag closed, in this case, isn't the main problem. It's just not helping, and if anything, hindering moisture evacuation. As neilmny's story illustrated, if you're warm enough but the rel humidity is high enough to make your feet sticky, a bit of air circulation fixes it.

Other angle is just get warmer, so the moisture evaporates effectively. In which case, cinch away!

Neo wrote:So, things I've been advised and somewhat experienced...

Full bladder, better to get up and pee as the body puts it's heat to the bladder and extremities get cold.



Nonsense -if you drank it and warmed it up before you go to bed, theres no reason the body has to 'put heat into it' over any other part of you. Different story if you skull a cold liter at 2am, hence why you should go to bed hydrated.

Neo wrote:Don't wear extra layers, use them to fill the voids in the sleeping bag. Your body heats the air space, so reduce it.


Half accurate - extra layers can compress insulation from the inside out and retain perspiration. Bag voids per se aren't the issue - its having that air pushes in and out of the bag as you move thats the problem. Filling voids with loose clothes isnt bad if they're loose and dry and compressible, but heavy, even slightly sweaty stuff can exacerbate common problems just as easily.
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Re: Feeling clammy when sleeping in cold weather

Postby Neo » Sun 22 Jul, 2018 12:03 am

Err, the body will try to maintain the bladder temperature, thus avoiding infection. Is there a doctor in the house to confirm?
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Re: Feeling clammy when sleeping in cold weather

Postby Orion » Sun 22 Jul, 2018 1:01 am

jdeks wrote:
Orion wrote:So you are saying that!

A warmer shell will lose heat to the environment at a higher rate than a colder shell. You can't have both higher heat loss at the shell and "a lesser rate of thermal loss" overall -- that's a contradiction.


Come on, man. Don't ask a question, then misquote the answer for the sake of making a contrary rebuttal. I made exactly that point in literally the next sentence.

jdeks wrote:Except usually it isn't[/i], for a number of reasons. ...

Secondly,[b] the outer shell radiates heat to the cold environment. The warmer the shell, the faster it does this. Conversely, the better the insulation, the slower it resupplies heat to the outer shell. Net result is, at a given ambient temp, an equilibrium loss rate with a colder shell. Probably.


So yes, more insulation = colder shell and less heat loss. Unless you OVER insulate but thats another scenario...

Takehome message here is that it's an interlinked multvariable system. It's not just "more x = more y".

Warin wrote:More insulation = less heat loss, less energy flow ..
The insulation from the outer surface of the bag to the heat sink does not change .. and the energy flow is less ..
So the temperature difference increases from the outer surface of the bag to the heat sink .. so the bags skin temperature will rise, not fall.

That different view help jdeks? Cannot reliably figure it for the heat source (inside the bag) as both insulation and heat flow change. Simpler to look from the heat sink, that way only one thing is changing.


...


Okay I'm goinna lay this out in a bit more detail. Whether folk read it is up to then, but dont come back at me unless you get to the bottom.




Heat energy creeps from the body outwards through the insulation, warming it as it goes. The speed of this is pushed by temperature difference, at first between the warm body and the inner skin of the bag, then between the warming inner skin and the first 'layer' of down, then between this layer and the next, and so on, right up to the outer skin.

As the outer skin finally receives heat energy, it too will warm. But - it loses heat faster, by convection and radiation to the cooler outside. It will heat a little, but tends to find balance closer to ambient, as the skin needs very little thermal difference to drive that radiation, but the outer insultion (being, yknow, insulative) needs a greater thermal differential to match in supply what the skin loses. That outer insultion will then also itself cool somewhat, choking its own transfer, until an equilibrium is established. This cooling will creep a little back up the insulation layers, and evetually establish a thermal gradient through the bag, with a heat loss rate to the outside defined largely by the insulation.


The specific temperatures of this gradient, depend on MANY things

Now, lets drop the outer temperature. The skin sgain radiates faster than it can draw from the outer insulation at first, and its temp drops, until it reaches a new point where the thermal diffrence draws as much heat fromthe insulation as it emitts by radiation. The outer insultion also cools accordingly, and a slightly steeper temperature gradient establishes in the insualtion. More importantly, the rate of net thermal loss only drops marginally - the reduced ouside temps have in turn lowered the insulation and shell temps, in itself moderating heat transfer rates.

On the inside, you probably barely notice - interior insulation and skin temps likely stay the same. This is, roughly speaking, the comfort rating of your bag.

Now drop the temperature more. Eventually, you reach a point where then skin simply cannot suck heat fast enough from the outer insulation to replace the rampagin radiation. What gets there may warm the skin fractionally, but that just accelerates the rate it radiates out, and it cools again until it ultimately approaches ambient. The skin just keeps leechnig heat out, until the outer insultion cools enough (ie also near ambient)to lower thermal drive to the shell and reach and new steady state, as it in turn draws heat from deeper in the bag. Eventually, it self limits as the increasingly cold insulation drives less heat outwards - but just when/where this happens depends on how cold it is outside and how hot the body inside is. You could end up with the skin, and several cms of outmost insulation all at ambient temps.

You can still feel warm like - in fact this is probably where most winter hikers are at. The overall heat loss isn't much less, and if the temp gradient doesn't lower too much, the inner insulation can still be at around body temp.

However- if ambient temp is at, or close, to dew point, this is one sceario where you can get condensate on, or in, your bag, depending on humidity. And if it goes too far, you then lower the temperature of your inner insualtion and inner bag skin. You feel 'cold', and any humidity, be it perspiration or otherwise, has no heat to vaporize it and drive it though and out of the bag wall (hence feeling clammy). This is the bottom end of your comfort rating, and this is where the OP is at.


Going much colder than this, and the temp differential will drive heat loss through the full insulation thickness faster than the human body can keep up with. You're just delaying the inevitable - how long for, is how you get the 'extreme' or 'survival' rating.

So now, lets increase the insulation. Skin's still ambient-cold and thus wont get colder, but the heat isn't leaking to it as fast . Ergo, the insulation warms up - first the inner layers, but then progressively to the outer layers. Some of this leaks to the skin, whih in turn radiates away, but it's slower because the insulation is better. The insulation builds heat until a new equilibrium is reached, this time with a much warmer insulation temp, as a much larger differential is needed to drive heat into the skin at the rate it then loses it to then enviroment.

Increase the insulation even more, and you can potentially hold so much heat that the bag skin will then warm, even with the consequent increase in radiant heat loss. In this case, you will indeed be losing more heat energy, but youd want to be - or you'd probably overheat. THIS is the other 'clammy' scenario - bag is borderline too warm and you wind up sweating inside then chilling. I doubt this is the OPs problem though.


So you're going to double down on this?

I didn't misquote you. You stated something that is physically impossible, not something that "usually" doesn't happen. You'd need to rejigger the laws of thermodynamics if you want a hotter body to emit less energy than a colder one. I thought you'd recognize that but instead you came back with a painfully long hand waving attempt to explain it all away. It was hard to read all that as it just dug the hole deeper.
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