Condensation in Super Shelter with VB or space blanket?

[BillyBob58]

Below are generalizations:

Condensation occurs when air comes in contact with a surface that is at or below the dewpoint. The dewpoint is always below the ambient temp. The reason is air can hold more total water at warmer temperatures. 70 degree air at 40% relative humidity has more water in it than 50 deg air also at 40% rh. That's why they call it "relative" humidity.

Cold air from the outside entering into the SS should not condense since all the parts of the SS are either at or above the ambient temp. Now the air in your sleeping bag is warm and can hold more water, which your body provides. As this air migrates through and out of the bag it reaches colder temps and may condense. The reason you put a vapor barrier close to the heat source is because you hope it will not get cold enough to cause condensation and at the same time prevent the damp air from traveling any further. If you put the vapor barrier after the insulation the humid air from the body will reach this cold impermeable wall and condense.

My guess is the SS gets condensation inside because a space blanket on top of the open cell foam insulation is not going to stop all the moisture your body produces. The moisture which gets around the SB gets trapped by the waterproof SS undercover and condenses on cold surfaces.

IMHO the SS would work better if it was made from breathable material, though it might get wet on occasion from heavy fog.

So OK, the points you are making above seem to be in opposition to those that MacEntyre was postulating: That cold air coming in from the outside might be the problem. And what you are saying is closer to my previous "understanding" of how this stuff works.

But as for the SB letting vapor through: that would surprise me. But I have never really tested a WM space blanket or Heatsheet for water proofing, I have just assumed it was there. I have found some few water drops on top of the space blanket, but not underneath it.

Have you ever tested your space blanket ( is it a Wallyworld special?) for being WP, by any chance? If mine were not put up in a box, I would go test them right now. I would be particularly interested to see if any vapor could get through with me trying to blow through it onto a cold surface.

If, as you suspect, body moisture can get past the space blanket, then I would expect it to condense down in the UC with it's cold material.

[Knotty]

So OK, the points you are making above seem to be in opposition to those that MacEntyre was postulating: That cold air coming in from the outside might be the problem. And what you are saying is closer to my previous "understanding" of how this stuff works.

But as for the SB letting vapor through: that would surprise me. But I have never really tested a WM space blanket or Heatsheet for water proofing, I have just assumed it was there. I have found some few water drops on top of the space blanket, but not underneath it.

Have you ever tested your space blanket ( is it a Wallyworld special?) for being WP, by any chance? If mine were not put up in a box, I would go test them right now. I would be particularly interested to see if any vapor could get through with me trying to blow through it onto a cold surface.

If, as you suspect, body moisture can get past the space blanket, then I would expect it to condense down in the UC with it's cold material.

I don't think the SB is letting vapor through but rather around. I'm confident that the SB is totally waterproof.

Silly Related Trivia: Bosch dishwashers don't use a heating element to dry the dishes. They use condensation. The Bosch gets the water very hot which then heats the dishes and the washer itself. After the water is pumped out the dishwasher's interior walls cool down faster than the dishes, so the water condenses on them. At any point in the "dry" cycle the walls are cooler than the dishes so the process continues unless you get impatient and open the door for a peak. This releases too much heat and interrupts the process. I was dubious, but it works amazingly well. No peaking allowed.

[BillyBob58]

I don't think the SB is letting vapor through but rather around. I'm confident that the SB is totally waterproof.

Silly Related Trivia: Bosch dishwashers don't use a heating element to dry the dishes. They use condensation. The Bosch gets the water very hot which then heats the dishes and the washer itself. After the water is pumped out the dishwasher's interior walls cool down faster than the dishes, so the water condenses on them. At any point in the "dry" cycle the walls are cooler than the dishes so the process continues unless you get impatient and open the door for a peak. This releases too much heat and interrupts the process. I was dubious, but it works amazingly well. No peaking allowed.

OK, so "around"? This may be correct, but: wouldn't moisture going around condense first on the top edge of the SS and even the top edge of the hammock on it's way to the pad and bottom part of the UC? Are you getting moisture there? With mt UC, the edges are actually in good contact with the hammock, almost a sort of seal.

Of course, it could go through the hammock to the SB and then out the sides, without having to first go by the SS and hammock edges. But my pad and SB are sort of wrapped around me, so it would first have to go up and then down into the UC. Possible I suppose.

Not trying to put these ideas down, I'm just being Devil's advocate and one of you guys may be right. I realize the bottom line is: you have condensation, even with the SB. Figuring out why is a challenge.

[Bumper]

I have to admit that I have real problems getting the ocf and SB lined up even reasonably close to where I'm laying, so it wouldn't surprise me if parts of the hammock were protected by the VB and other parts weren't. Still, the amount of water in the bottom concerned me.

Just a thought: I always pull the snakeskins back over the ends of the hammock to stop the lines getting wet, and to form a kind of seal over the hammock ends but I'm wondering if that just acts as a giant funnel to channel cold air into the hammock and UC? Maybe that might contribute to the problems?

[MacEntyre]

...wouldn't moisture going around condense first on the top edge of the SS and even the top edge of the hammock on it's way to the pad and bottom part of the UC?

It would, if the temperature difference were there. I don't think the top edge gets warm enough.

[Knotty]

In a tent, almost every surface is a condensation point (provided your in a situation where the factors are right for condensation) but you can minimize or eliminate it with proper ventilation.

In a hammock, everything except underside insulation is well vented by default, so we usually don't get condensation. Using an over cover is a different story, then you're pretty much in a tent. Adding a SS also kind of creates a mini tent area with little to no ventilation. With no SB for a vapor barrier, you're putting a good amount of moisture into this unventilated tent. I think we all agree that's a problem but I'm still having a hard time understanding how warm moist air is getting around the SB if you do use one.

I wonder if the SS would benefit from putting a vent along the bottom edge? Would this allow moisture and even condensation to escape yet still protect the insulation in heavy fog? Or more importantly, is it possible that the SS was designed to be non-breathable so that the humidity underneath the sleeper would increase, making you feel warmer with less insulation???

[BillyBob58]

........With no SB for a vapor barrier, you're putting a good amount of moisture into this unventilated tent. I think we all agree that's a problem but I'm still having a hard time understanding how warm moist air is getting around the SB if you do use one.

Me too. It seems like it would have a tendency to rise ( being warmer) unless it managed to get through the VB first, and hit a cold surface down there.

I wonder if the SS would benefit from putting a vent along the bottom edge? Would this allow moisture and even condensation to escape yet still protect the insulation in heavy fog? Or more importantly, is it possible that the SS was designed to be non-breathable so that the humidity underneath the sleeper would increase, making you feel warmer with less insulation???

Well, I'm pretty sure the UC, as well as being intended to keep outer rain and wind out, is meant to allow "warm" air to be somewhat trapped. I don't think it was meant to keep "moist air" in, hence the manufacturer suggested SB. But, who knows? And a vent would allow (maybe) moisture to escape but might let more heat out with it. If you could prevent condensation, it might be worth it.

But this is still theoretical for me, as so far I have had no problems. If I was going to have problems, you would think I would have had them in the rainy/foggy/misty Olympics in the 40s and 50s. And I did, but only on the first night when I didn't use the space blanket.

[MacEntyre]

There are two facts that might simplify all this philosophy...

1. vapor barriers do not allow moisture to pass.

2. neither hammock nor hammock insulation is air tight.

I think if you chase leaks, or air channels, some of which open up only when the occupant moves, you will find the cause of condensation below the vapor barrier.

[Knotty]

It seems like we're pretty much in agreement at this point. Now it's just a matter of solving this occasional problem.

[Ramblinrev]

It seems like we're pretty much in agreement at this point. Now it's just a matter of solving this occasional problem.

put drainage holes in the undercover... or carry a sump pump?