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.jdeks wrote:Whats the loft in your down bag like the next morning?
And what was the overnight humidity?
wayno wrote:...then the moisture from the air above descends to ground level to concentrate...
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,
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,
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.
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
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?
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
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.
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.
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.
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.
Neo wrote:Full bladder, better to get up and pee as the body puts it's heat to the bladder and extremities get cold.
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)
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.
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.
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?
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.
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.
Isn't less air space better?Neo wrote:Theory there is your body heats up the bag airspace rather than the layers.
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.
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.
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.
Huntsman247 wrote:Isn't less air space better?Neo wrote:Theory there is your body heats up the bag airspace rather than the layers.
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?
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.
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.
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.
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