Are breathable fabrics less prone to condensation.

[Matt Dirksen]

Come to think of it….

One could sew in "Packtowel" material for the ultimate in breathability and condensation management. ;>D

Of course it would just LOVE to absorb all that rainsplash that would occurr at the edges of the rain fly as well. I wonder what would happen to a pack towel if one side were sprayed with a water repellant? Perhaps it'll work for 5 minutes? Maybe 10?

SO, how about a nice tent fly gutter & downspout system to control where the rain runoff occurs. (I've seriously imagined this: fold the fly seams up & over then sew in a thin rope that'll magically wick up the water & and drip it out at strategic locations – down guy lines that are tied to the rope.)

I'm "letting the tail wag the dog", a little. Sorry for the thread drift (pun intended.)

[Jerry Adams]

If the outer material goes closer to the ground, there will be less splash.

If there is condensation on the inside of the outer material, it will tend to run down and drip onto the ground

If there is condensation on the inside of the bathtub wall, it will tend to run down, onto the floor, and get absorbed into your sleeping bag

[Matt Dirksen]

Thanks Marko,

That makes complete sense to me, and helps me better understand why "parts" of a tent behave differently than other parts.

Like our buildings: all four walls of a completely exposed home behave very differently to vapor drive, even if the wall materials are all the same. Due to both the solar exposure on each wall coupled with different "uses" on the inside of the walls (esp. kitchens & bathrooms.)

If the capability to dry out was valued and respected as much as the desire to not get wet, we'd have many more comfortable shelters, I believe. Both homes and tents alike.

[Jerry Adams]

Static ideas like phase diagram or dew point are fairly straightforward.

It's easy to figure out where it will eventually stabilize to.

But the dynamics of how it gets there is very complicated. No easy formulas. Chaotic behavior.

I like the idea of looking at different surfaces on a cold morning when there's dew.

[Marko Botsaris]

"SO, how about a nice tent fly gutter & downspout system to control where the rain runoff occurs. "

It may be a humorous thought, but experienced tarp user already do this. For example if there is a spot where a tarp drips in a pinch you can attach a (drip) line and arrange for the water to slide down the line somewhere else harmlessly.

I don't want to make an absolute statement about the products without knowing for sure, but I believe, for example, the surfactants you buy for the inside and outside of you car windshield are different. They are certainly marketed that way.

The gunk you put on the outside encourages big droplets – hydrophobic (neutrally polarized electrically). The droplets don't stick, and roll off easier when it is raining. On the other hand the stuff you put on the inside to prevent fog I suspect are hydrophilic. In this case at the surface the condensing water will tent to spread flat, this increases the surface to volume ratio and so should make it harder for drops (fog) to condense. Although it this is the case it would have to be only just hydrophilic enough I suppose. The effect can cut both ways. By analogy, if you spray or otherwise treat the inner surface of a tarp with such an "anti-fogging" surfactant, it might improve the condensation problem.

I don;t know if anyone has experimented with this much, but it likely would not work with anything formulated for glass.

It also could depend on the shelter design as in some case the whole strategy would be to have the condensation slide harmlessly to the side a la a Hexamid with a screen (or no) floor. In a case like that a hydrophobic surfactant might work – though probably not I guess.

In the case of breathable fabrics you would probably heavily mess with its properties by applying anything ling that.

[Daryl and Daryl]

Matt,

"But because the nylon walls will allow for a (slightly) warmer climate in the space where you are sleeping, the vapor will also drive out to the coldest areas around your shelter"

This is what keeps my small myog, tents pretty dry inside, even though I add no vents and even though it feels quite humid inside the tent. I make the inner tent out of solid uncoated fabric and as small as I can tolerate. The outer is coated. Condensation usually occurs on the fly only. The other big plus for me is that it warm and cozy inside the tent.

I used to have an all fabric Gerry tent where the waterproof bath tub wall floor was sewn to the uncoated solid nylon tent wall at a point about 4" above the tent wall bottom. So there was a double wall for the first 4 inches of the tent bottom (coated bath tub wall + uncoated tent wall). This double wall design kept the bath tub wall warmer than if it had been exposed directly to the air……and it got very little condensation at night.

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