Cuben = Low Condensation?

[Miles Barger]

I recently bought my first cuben shelter (an MLD Patrol in .74 oz/yd green cuben). I got it for the weight savings, but there seem to be other benefits. The most welcome change I've noticed is very low (actually no at this point) condensation.

This (great) BPL article on the causes of night-time condensation on shelter material is enlightening. My main takeaway is that, while available moisture will have an effect on how much condensation occurs given the right conditions, the force causing water vapor to condense on the material surface in the first place is its temperature being lower than the ambient air temperature. And it seems like the greatest driver of the temperature differential is radiant cooling of the material. Thus, my hunch is that the cuben laminate has very low radiative heat loss and/or a low heat capacity, such that it strongly tends to stay at ambient air temperature.

Does anyone have data or measurements to explain the potential reasons why this might be the case or to call total BS and give a much better explanation for this phenomenon that I (and others on the forum) have experienced?

[Daniel Fish]

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[Miles Barger]

Yeah, the high airflow compared to a completely enclosed shelter surely helps. I've had it pitched fairly low on near-windless nights close to freezing, though, and had zero condensation (not my experience with silnylon), which is what makes me wonder if something else is going on.

[Daniel Fish]

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[Dan @ Durston Gear]

Cuben does empirically seem to have less condensation. Not sure why. It could occur because cuben has a lower density (or really lower specific heat capacity) than silnylon, so when warms air inside the tent hits it, the air doesn't cool/contract as rapidly.

[Nelson Sherry]

Two things I can think of that may play a roll in condensation.
1) Poor heat conductivity between the inside and outside surfaces.
2) Having a surface of the fabric that is slightly more hydrophobic than other fabrics.

A differences in heat capacity doesn't make sense since amount of heat in the material is going to rapidly achieve a steady state with the average outside/inside air. It's the rate the temperature changes between the inside and outside of the material (if it does change) that would matter, and that is heat conductivity, not heat capacity. I would argue that the insulation value of the material is so tiny that even a difference in heat conductivity doesn't make sense as an explanation.

However, surface properties that enhance or diminish condensation/evaporation is likely. If one material tends to hold onto water molecules (hydrophilic) while another tends to repel them (hydrophobic), it is likely that condensation will occur more rapidly and abundantly when the material itself is helping hold the water molecules together. And, evaporation of the condensed water will occur more rapidly on a surface that is not holding onto the water as tightly?

Maybe cuben fiber has a surface more like my eyewear after I apply an anti-fogging agent?

[Ben C]

Maybe the materials have different levels of emissivity. If the nylon has a higher emissivity, it will radiate more heat to a clear sky, and it will get cooler and get more condensation. My best theory. But I couldn't find emissivity rates on the materials.

[Tom Lyons]

I think it's conditions related and conditions you have experienced with it so far were not conducive to condensation issues.
I suspect it's coincidence, and has nothing to do with materials.

[Franco Darioli]

My lawn at this time of the year produces an enormous amount of condensation.
Side by side the fly of a double wall tent is just as wet as the one form the single wall type (of course…)
I would like to have the same design in Cuben and silnylon side by side to see what happens.

[Travis Leanna]

>I would like to have the same design in Cuben and silnylon side by side to see what happens.

Time to get on the horn with Henry and start pushing for some cuben shelters, right?

:) I kid, I kid.

But I'll add to the empirical evidence of cuben seeming less condensation-prone.

[David Ure]

Nah. The condensation is the same. The difference is that silnylon absorbs a bit more moisture as the droplets cling to it. Silnylon is extremely sticky. With the cuben any moisture probably rolled off. Plus there likely wasn't the right weather conditions for condensation to accumulate.

[Greg F]

A difference in emmissivity would cause a difference in condinsation. The higher the emissivity the higher the rate of energy loss and cooling. Condesation occurs when the water vapour in the air condenses and tranfers its energy into the tarp to keep it in thermal equilibrium. Therefore the higher the emmissivity the higher the condensation.

Now we just need to find out the emissivity of mylar and sil to see if there is a significant enough difference to explain the effects.

The aluminized mylar heat sheets have low emmissivity so comparing sil to aluminized mylar would be a good experiment to see if fabric emmissivity has a real effect on condensation.

[David Ure]

Sure…if you were wrapped up in cuben like a burrito and your body was radiating heat. In this case, the OP was under a tarp, pitched high, and therefore emissivity is not even a consideration. There is no way his body temperature was enough to push up the dew point.. It is likely there was sufficient wind to take away the condensation assuming the conditions were right in producing it in the first place.

[Greg F]

You dont need a heat source,

The tarp radiates heat at its black body temperature cooling below the ambient temperature of the air. The latent heat of condensation warms the tarp until an equilibrium point is reached between the cooling affect of radiation and the warming effect of condensation.

If emissivity is lower less condensation occurs.

[Jerry Adams]

http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html

unfortunately, all they have that's relevant is that "plastics" are 0.91

so, maybe nylon and mylar are 0.91

aluminum foil is 0.04

so maybe there's no difference between silnylon and mylar, but aluminized mylar would lose much less heat to a clear sky so it would be a little warmer so less condensation

[David Ure]

Looking at only one factor misses all the others: how quickly temps dropped, whether the OP was pitched close to a water source, whether it had rained in the last 24 hours and whether the ground had any moisture remaining, whether there was any wind, etc.

What you are suggesting is that emissivity would allow cuben to not produce ANY condensation. It would also limit its use as a vapor barrier, which we have seen is not the case.

[Greg F]

No, I am saying its possible that the emmissivity of the fabric may play in a role in the anecdotal reports that cuban fiber has less condensation than Sil. I think it would be worth finding emissivity data or experimenting with side by side identical shelters to see if it is possible.

[Serge Giachetti]

I'm not even going to speculate why, but I've had almost zero condensation problems with my hexamid cuben after having significant condensation with two previous sil shelters. 100's of nights in both materials, I don't think its a coincidence. My friend had the same experience with his cuben shelter hiking the CT.

[Roger Caffin]

> zero condensation problems with my hexamid cuben after having significant
> condensation with two previous sil shelters.
On the other hand, that could be entirely due to the design of the shelters.

Cheers

[Tom Lyons]

On the table of Emissivity, the listing for "clear silicone" is .080-.100.
The listing for "plastic", and mylar is plastic, is .95-.100.
So, on just a materials basis, it's close, and there is some potential for the silicone to have lower emissivity.

However, the surface finish plays a part in IR emissivity, and very polished or slick surfaces tend to have lower emissivity than rougher surfaces, so the mylar might have some advantage in that area.

In terms of color, darker colors generally have higher emissivity than lighter colors, so if the shelters are different colors, then it might make some difference.

My guess is that if the shelters are both light colors, it's not really an issue of materials because they are too similar in emissivity to really make that difference. If the cuben is light colored and the silnylon is dark, that might make the biggest difference.
I still think it would be marginal at most, and probably no real difference, in terms of materials. Conditions would be much more of a factor.

[J-L]

I'm with the emissivity people. I've found that limiting my tent's exposure to the night sky (so limiting the effect of radiative heat loss/emissivity) can significantly reduce condensation.

If someone has a cuben tarp and a silnylon tarp, it would be neat to pitch them in open areas at night and measure their surface temperatures. This would provide a relative reference point for comparing their emissivity values.

[Jerry Adams]

Emissitivity is in a range of 0 to 1

If it's closer to 1, then a surface will radiate more heat away to a colder area, like the clear night sky, so it will get a few degrees colder. If it's a few degrees colder, there will be more condensation, but it depends on the humidity and maybe the wind

[Peter Fokkinga]

As a counter point, I experienced plenty condensation with a cuben Duomid. Used an Oooknest inner too, essentially turning the Duomid into a double walled shelter. I'd say the temperature during the day was about 65 degrees, dropping to 40 (or a little less) at night. Humidity was generally pretty high (this being Norway).

[David Ure]

"No, I am saying its possible that the emmissivity of the fabric may play in a role in the anecdotal reports that cuban fiber has less condensation than Sil. I think it would be worth finding emissivity data or experimenting with side by side identical shelters to see if it is possible."

I agree that it could be a small factor but the OP has not experienced any condensation, so we have a number of drivers presenting themselves here.

[Franco Darioli]

I have had all sorts of shelters made with different fabrics (polyester/various nylons/silnylon/ sil with PU coating,PTFE (ToddTex),Epic,Cuben, Tyvek …) set up overnight on my backyard.
My observation is that if in the morning the grass is dry, the shelters will be dry , if it is wet (from evaporation not rain…) the shelter will be wet in about the same proportion
(the wetter the grass, the wetter the shelter)

Not long ago just as someone boasted that his (expensive but not Cuben) shelter had ZERO condensation, another one here at BPL called exactly the same shelter a "condensation machine"
Not that it is an unusual situation. I have seen many seemingly contradictory comments before*, the point is that, unless you have side by side comparison (say two 8×10 tarps and or two shelters of the same design) and with a person (or two) inside of similar size and metabolism , everything else is just conjecture.

*One of my favourite;
a) The shelter remained "bone dry" , only two tiny water drops on the floor.
b) I had "puddles" on my tent floor the next day.

Those tiny drops and those puddles were (from photos) about the same size. Different shelters and simply a different way of looking at the same result)

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