Help me! - understand cold weather condensation

**Take-a-knee** · 10-29-2007, 20:44

Turk, that camo outer bivy is goretex top and bottom, every part of it is breatheable.

**warbonnetguy** · 10-29-2007, 20:59

gore tex is only very slightly breathable though. probably closer to silnylon than to uncoated ripstop

**Peter_pan** · 10-29-2007, 21:16

Originally Posted by warbonnetguy

i'm wondering if how warm/cold you are might effect this too. try using just enough insulation to keep you warm. especially on the bottom. you may notice less condensation.

laying directly on a vb like jeff said, instead of having one under the insulation, would keep moisture from reaching the insulation in the first place, and your body could still evaporate moisture out the top of the system.

also, once the skin on your back gets clammy enough, your skin stops perspiring/giving off water vapor. this is why a ccf only gets so wet. with your setup, the moisture isn't right against your skin, so your skin stays dry and keeps passing water vapor through the insul, till it stops on the other side. i think i got this from the warmlite site, but basically it said that you will only keep passing water vapor if it's going somewhere, if you skin isn't evaporating it, the evaporative cooling mechanism stops. with your setup, it is going somewhere, just not far, but far enough that you probably pass alot more water vapor than if the vb was right against your skin or shirt.

WBG, et al,

Be careful borrowing info from the ground community....Once condensation/sweat pools start on a pad or above a vapor barrier, in a Hammock, little if any can evapoate upward due to the wrapped up sides which by the nature of the hammock are fairly tight agaist the body.... In fact all this extra seal against the body, which does not happen to ground guys on flat pads, exaccerbates the sweat/condensation issue.

Also, the part about the body slowing/stopping prespiration once it is clammy damp is also stated relative to the flat ground... In a general sense this is true.... The Catch is that in a hammock there is a quick runoff of excess sweat/condensation to form a pool at the low spot... under the butt/lower back.... It is this pool that will wake most folk repetitively for the bio break....This is a real cold weather issue as moisture robs heat faster than air.... and... the body can not keep the bladder warm enough if it is attempting to keep this undesirable pool warm also.

Pan

**warbonnetguy** · 10-29-2007, 21:49

i was talking about your body still being able cool itself by evaporative cooling through the top of the system. the top of the system being the breathable sleeping bag on top of your body. i agree, any water vapor coming out of your back has no way to escape if there is a vb underneath.

as for the skin reaching a saturation point and ceasing to pass vapor, i don't see what this would have to do with flat ground vs a hammock.

also, all my experience with condensation of a ccf pad has been that the pad is wet where my body was touching it, not that it pools at a low point. it's no wetter under my butt than it is under my shoulders.

as far as moisture making you colder, you're right, moisture does rob you of heat faster. as far as i know this has to do with evaporative cooling. your body uses heat and energy to evaporate the water when you get wet, but in the case of a vb, the water cannot evaporate and as result, no heat would be lost this way. this is the whole point of the vb. what you are talking about (moisture robbing you of heat) would only happen with breathable insulation, like a wet uq, where the moisture could evaporate and take heat with it. that's how i understand it anyways.

**Just Jeff** · 10-30-2007, 05:44

But if your back is wet, then you roll over and expose it, you get chilled.

**warbonnetguy** · 10-30-2007, 19:23

good point, you would need a full coverage vb to keep that from happening.

i'm still trying to figure out why i've never had condensation issues with my sil uq, even when the top of my down bag is wet and the bottom of my tarp, and in a wide range of temps (40's-20's), the uq has always stayed dry. it eludes me. maybe it has something to do with the slight inefficiency of an uq alowing some breathability. the hammock itself doesn't really collect condensation either. there is obviously a very complex set of variables involved with condensation, which can drasticly effect comfort and warmth, and breathability isn't necessarily the end all solution, (hence the wet down sleeping bag, which has happened more than once., usually in colder conditions).

**Just Jeff** · 10-31-2007, 05:44

Yep - that's a tough one. I never had condensation problems in the Crazy Creek either, and it has a non-breathable bottom. I used it in ~35-55 F, sometimes with humidity.

And I've never had sweating problems with the Exped Downmat 7. Even when I was slightly too warm, a little top venting solved the problem and I never got clammy from the pad.

**sk8rs_dad** · 10-31-2007, 07:24

Originally Posted by warbonnetguy

i'm still trying to figure out why i've never had condensation issues with my sil uq,

You may be over-insulated.

I stumbled across this article by Dr. Gordon Giesbrecht (Dr. Popsicle) of the University of Manitoba that tries to explain cold-weather clothing design. The trick is retain enough heat to stay warm, but allow enough heat to escape so that condensation happens beyond the vapour barrier.

"it is VITALLY IMPORTANT that water vapor pass through the clothing layers before condensing into liquid form. If condensation does occur, liquid moisture must reach, AND PASS THROUGH the outside layer of the clothing before it freezes. In a cold environment, the moisture may freeze and be trapped within the clothing." (Giesbrecht)

**kohburn** · 10-31-2007, 07:30

Originally Posted by warbonnetguy

i'm still trying to figure out why i've never had condensation issues with my sil uq, even when the top of my down bag is wet and the bottom of my tarp, and in a wide range of temps (40's-20's), the uq has always stayed dry.

if the vapor never makes it far enough through insulation to cool to the point of condensation, and is allowed to pass through just fast enough to avoid reaching the saturation point then you'll never see/feel it. also naturally most of the warm vapor will rise and pass through your down top condensing in or ontop of it. with a CCF pad you get absolutely no breathability down so if the vapor is trapped under your body it will build up till the air space reaches its saturation level and drops the moisture out of the air.

for the sake of maximum heat a vapro barrier works well, but it lacks in the comfort area if you end up wet, so really the ideal is a vapor retarder that slows the transfer of vapor to the outside air to both retain as much heat as possible but also allow enough diffusion of moisture to avoid condensation inside the bag, inside the insulation, or on the outside of the bag.

so it sounds to me like your underquilt is simply providing the right balance of breathability with insulation.