Help me! - understand cold weather condensation

[turk]

Hey folks,

I am experiencing a problem that seems to be mounting worse and worse as the season gets colder here. Hopefully someone here can tell me exactly what is happening and what I need to do to correct it.

I am using my new high peak simex panda hammock. Which for those that have not read that thread is basically a hammock with sleeping bag permanently attached. The outer shell of the panda is a DWR coated ripstop nylon. Outside of this is another layer of DWR nylon that runs full length and serves as a pad pocket. The insulation for the hammock is synthetic and is inside the hammock. (Yes you compress it when you lay on it).

Inside the hammock I am using 2 parts of the US ARMY standard issue Gortex version partrol bag. (3 piece bivy/bag combo) - I got from Take-a-knee. Against the inner shell fabric of the panda hammock I am using the waterproof synthetic bag from that set. Inside of that I am using the black inner bag which is breathable. This will simulate a cut-away cross section view of how my layers are stacked:

P = pad pocket sleeve on panda hammock (DWR coated ripstop - not insulated, not using any pads)
X = panda hammock bag (synthetic insulation .... this is the problem layer getting soaked on bottom only)
0 = army outer bag (DWR coated ripstop synthetic insulated)
U = army inner bag (breathable nylon, synthetic insulated)

XXXXXXXXXXXXXXXXXXX
X 000000000000000 X
X 0UUUUUUUUUUUUU0 X
X 0UUUUUUUUUUUUU0 X
X 000000000000000 X
XXXXXXXXXXXXXXXXXXX <--------- This is the problem layer right now
PPPPPPPPPPPPPPPPPPP


Here is the problem. When I wake up in the morning, I am getting major!! condensation between the insulation layer of the panda hammock and the outer layer of the DWR army outer bag. I honestly thought someone was playing a joke on me. It was as if someone dumped a large container of water into the hammock. It was in two places. A large circle 20" dia that was roughly from my hips to my shoulders, then a bare dry patch, and a smaller aprox 10 dia circle about where my feet were.

Using the above diagram will help explain better. Layer PPPPPPPP is bone dry. One layer up from that XXXXXXXXXXXXX is absolutely soaking wet by morning. I would estimate a pint of water or more this morning, drenching the bag. One layer up the bottom layer 00000000000000 stayed dry because it was DWR ripstop. I am not currently using any CCF pads in the pad pocket of the hammock.
I am trying to establish how low I can get this setup before I have to add pads to the bottom insulation, and better calculate how much warmth one layer of 3/8" CCF will add.

here were my weather conditions for last night:
-2 deg C, 50km/h wind, 80% humidity. Light rain/freezing rain during day.
One hour rain storm at aprox 11pm. No precip beyond midnight.

Worth mentioning. I did not sweat at all during the night. I was at perfect sleeping comfort, breathing outside of bag, and aprox 1/4 unzipped for ventilation. In past weekends I noticed this moisture, but chalked it up to my own sweat, and overheating myself in
the night. I know now for sure this is not the case.

So ..... what is causing my serious condensation issue?
How am I getting that first bottom layer of insulation so thoroughly soaking
wet, and yet no visible signs of moisture anywhere else. I think it has something to do with the pad pocket and the fact that I am not using a pad in it. Can anyone explain to me what is happening ?

I would have thought that the inside of the pad sleeve would have been wet. And I certainly expected the DWR nylon on the outer shell of the US army outer bag to be slick with moisture, yet it was completely dry. But somehow my bottom and first insulation layer which is the hammock layer is getting wetter and wetter as night time temps drop, and I add layers to my system.

[Just Jeff]

By waterproof I assume you mean wp/b - like the goretex bivy? If that's the case, here's what may be happening. Moisture condenses at a certain temp. In a sleeping bag, that temp is often reached at a certain point inside your insulation...so that's where condensation occurs.

Think of it like this - the inner layer of your sleeping bag, against your skin, is much warmer than the outer layer of your sleeping bag, which is open to the elements. When the condensation point occurs between those two temps, your bag will have condensation inside.

The same thing happens with underinsulation, assuming all of your insulation is breathable.

Does that make sense based on your setup?

[turk]

okay, I think I get it. To clarify, the one layer of the US army setup I am
NOT using in this equation is the bivy sack layer because I know it is non
breathable. The next layer which is the outer bag, has a DWR coated
ripstop... I don't know exactly how that rates for breathability

Is this the layer that I need to swap out to a different more breathable bag?
Is there any way to eliminate the condensation build up completely, or will
swapping this layer out make condensation then occur inside my pad pocket
which is my final non breathable layer?

I am afraid to swap any of my layers to my more breathable down bags until I understand
what is causing the problem, and that i have it licked, lest I do considerable damage to
the loft of the down.

[Just Jeff]

DWR is a pretty good mix between water resistance and breathability. Depends on the treatment of that individual fabric, but DWR generally tends to pass moisture pretty well.

The pad pocket is non-breathable? That's your problem - it's a VB, so moisture can't pass beyond it. Any non-breathable insulation between you and the VB will retain your body's moisture. I'm surprised that the moisture isn't between XXX and PPP...must be due to two things. First, the temperature gradient in the other post. Second, DWR is not waterproof but it does prevent some moisture transfer, and the insulation inside it is like a sponge...so coupled with the temperature gradient, that's what collects the moisture.

At least that's my amateur opinion!

Two solutions - replace the non-breathable pad pocket with something breathable, or add another non-breathable layer between your body and the insulation. Like putting your insulation in a sandwich bag. Now your insulation will stay dry, and there won't be as much moisture b/c your body will stop sweating sooner (research how VBs work on www.warmlite.com).

But right now, your non-breathable pad pocket is acting like a VB, and putting insulation inside a VB is a no-no.

[Rapt]

The problem is common with WP/B fabrics on the outside of insulation. They work be being breathable to vapour but not to liquid water. Often if they are the outside of the insulation they're cold enough for the water vapour to condense on the inside face before it passes through.

If you put more insulation outside of the wp/b it'll pass through and then condense either in the outer insulation or on one of the fabric faces outside it.

If the pad pocket isn't breathable then its going to collect there more than elsewhere.

As you probably know even if you don't sweat a drop, your body still transpires a fair bit of moisture through the skin. See here.

If you can make the pad pocket area breathable and possibly insulate it a bit more outside the pad it will likely solve your problem. Right now the temperature there is low enough for the moisture to condense, it has to be, even if its non breathable, raising the temperature at that point in the system will help. You do this by putting more insulation OUTSIDE of that area....

Or as Just Jeff says, go to a VB liner.

[kohburn]

Moisture condenses at a certain temp. In a sleeping bag, that temp is often reached at a certain point inside your insulation...so that's where condensation occurs.

at warmer temps that will happen closer to the outside skin of the bag. as the weather gets colder the cold temps will move inward so the colder it is the closer to your skin the vapor will condense.

[Peter_pan]

Turk,

Sounds like the WP pad pocket is the issue....it is most likely the cold point where the evapoating moisture is condensing into the liquid again.... Just like the top side of a silnyl tent... cold night air cools and condensed the rising evaporation... same thing happens on the bottom... and to exaccerbate the problem, it collects in the "tub shape" of the hammock bottom.... with less over you, earlier in the year, you may have allowed some more to rise and evaporate (thus the managable issue you described) vs trapping even more moisture below you in a winter rig...It really is important to have a breathable bottom as well as the breathable top to avoid condensation issues....

This is the point I have cited for years... the moisture that does not evaporate is packed and carried the next day.... it is just that most folk can't notice 4-8 oz more weight and the average one to two day trip doesn't necessarily become obvious... but it is there.


Pan

[Rapt]

This is the point I have cited for years... the moisture that does not evaporate is packed and carried the next day.... it is just that most folk can't notice 4-8 oz more weight and the average one to two day trip doesn't necessarily become obvious... but it is there.


Pan

Another really good point.

[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.

[nogods]

most quality tents have a draft window near the bottom of at least one wall that you can unzip to allow air to flow in to aid in moving "wet" air up and through the breathable "roof" of the tent. Hammock manufacturrers should design similar vents in the far foot end or head of their hammocks.

For condensation caused by breathing you can cut a hole in an oxygen mask, insert and duct tape a flexible hose to it, then run the hose out of the hammock to eliminate condensation from your breathing...