CD stipulate on their website inflating the Neoair series of mats by mouth poses no issue in so much as long term degradation of the mat AND insulation....
Although I feel comfortable with the statement regarding long term durability (especially as I live in a warm climate so for the most part my mat will eventually dry at home from whatever residual moisture there was in it)

But what about the latter part - does it makes sense that humidity from breath will not negatively affect the R value of the mat AT THE TIME OF USAGE - namely that even if there is some condensation inside the mat from the humidity in my breath it will not adversely affect R value on that night or subsequent nights on the trail?
How can that be? Obviously water (or ice) has much higher thermal conductivity than air....so one would assume it would degrade performance. Taken to the extreme - if i would fill the mat with water.....

Thoughts?

From my understanding, moisture really only affects insulation with loft. There is no traditional insulation in the neoairs, only air chambers which restricts thermal conductivity by limiting airflow.

That's how it makes sense in my head at least.

I guess it depends on the insulation used in the pad. If it uses baffles like a lot of newer pads, the moisture may have little difference, but if it uses puffy fibers, I'd assume moisture would have more of an effect.

Another thing, no matter how bad it effects the insulation, the accumulated moisture should over time add to the weight of the pad.

"...does it makes sense that humidity from breath will not negatively affect the R value of the mat AT THE TIME OF USAGE - namely that even if there is some condensation inside the mat from the humidity in my breath it will not adversely affect R value on that night or subsequent nights on the trail?"

Regardless of the physics of convection and heat content of dry versus humid air, keep in mind that these pads perform well in the Pacific Northwest, Georgia, and Missouri, USA, where 98% humidity and cold temperatures are not uncommon.



"Obviously water (or ice) has much higher thermal conductivity than air...."

True. But you don't have a continuous liquid (water) or solid (ice) path. It is very small (and discontinuous) compared to the thickness of the pad. And, assuming the volume of a Neoair is about 0.10 cubic meters, the air can only hold about 1.2 grams of water. Not a lot of thermal mass.



Degraded? Yes.
Significantly? I doubt it.
Hoax? Well, maybe not 100% "truth in advertising", but not the Brooklyn Bridge.

Edited by greg23 on 02/01/2013 09:21:59 MST.

This made me curious about the humidity of exhaled breath. The web site states the average as 35c and 95%. There is an interesting calculator for condensed breath (the point of the web page).

http://www.sciencebits.com/ExhaleCondCalc

Given typical PNW conditions, that's about the same as atmospheric humidity. It seams the only way to improve on it would be to use CO2 or other canned gases.

I wonder what humidity stored air mattresses stabilize at? Would hanging them with the valve open and slack inflation allow them to dry? An accurate scale (lab grade) and weighing one over time would tell the tale on moisture accumulation.

"I wonder what humidity stored air mattresses stabilize at? Would hanging them with the valve open and slack inflation allow them to dry? An accurate scale (lab grade) and weighing one over time would tell the tale on moisture accumulation."

The recommendation by Big Agnes for their Clearview pads is to hang them with the valve open. I have watched the water run down and then disappear.

As mentioned above, 1.2 grams of water is a (many assumptions) theoretical maximum. Cool dry central Rockies outside air is around 15% RH. Inside a house it is closer to 50% RH. So, guessing, I (in Colorado) might see a half of a gram weight loss as 100% RH air is replaced by 50% RH air. In the Pacific Northwest or the Southeast, I would assume even less of a difference.

But that is for One night out. For each night out, in a condensing situation you could, theoretically, add about a gram a night. I have no clue on how much water vapor would be held by the outgoing air in the morning. Doing pre and post drying weights could be interesting, especially after a 10 day trip.

Edited by greg23 on 02/01/2013 10:32:06 MST.

I read where an outdoor gear rental company uses a vacuum cleaner to inflate sleeping pads with dry air when they get returned.
This supposedly reduces the moisture build up somewhat.

Be aware that 95% humidity coming from breath is measured at near 99 degrees temperature. That is much higher water content than 95% at cooler temps.

Compared to a 95% humidity ambient air on a cool night is a big difference.

Filling a mattress with the cool ambient air will be much drier than your breath.

I've been weighing my Prolite. It's weighed the same, within about 0.1 ounce, since last May. About 50 nights. That is, I blew it up 50 times. About 3 breaths each time.

I have to let the outside dry out first - that can add a couple 0.1s of an ounce.

Neo-air requires more breaths, but still, I don't think it's significant.

You could weigh your Neo-air, and occasionally weigh it again, and if it doesn't increase in weight, you're okay.

Going with the 1.2ml of total moisture going into a Neoair, one can calculate the total effective conductance of a two layer material in series (i.e. http://www.nzifst.org.nz/unitoperations/httrtheory2.htm). Grabbing some values for air and ice ((http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html), I calculate that the change in effective conductance is between 1-2% (source code for a matlab calculation here: http://pastebin.com/d6zd2d3B).

I say we boycott.

Wasn't one of the issues relating to how the humidity was causing the aluminum baffles to flake off? I'm pretty sure that was someone's anecdotal observation in a post here on BPL.

EDIT. Yeah, heres the link:
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=63495&disable_pagination=1


I have never been concerned with how my breath affects the r-value immediately, but I have been concerned that it will lead to the breaking down of the baffles (which I guess affects r-value in the long term). I got an instaflator for this reason.

Edited by Konrad1013 on 02/01/2013 14:27:06 MST.

Konrad's right. At one point, on a really wet hike this summer, I watched the moisture collected at the head of my pad rub the aluminum coating off of the baffles inside as I deflated the pad and tried to roll it up. Given the translucent XLite fabric, it was easy to see as it happened.

FWIW, I'm not sure that the loss of the reflective coating affects the R-value too much. The baffles are what really insulate.

The question I have about the flaking is that do the original neo airs flake but we just cant see it or is this something tat only happens with the new neo airs. If it happens on both then is it really an issue? I have never heard a complaint about an old neo air getting colder with age.

Flaking foil has a large effect on effective R value

If just a few places flake not a big deal

Greg, I don't think the old NeoAirs had the same foil coating. Could be wrong about that though.

Honestly, given the numbers when the original version pads were tested, they seem to be under-spec'ed rather than over when it comes to R-value.

" ... inflating the Neoair series of mats by mouth poses no issue in so much as long term degradation of the mat AND insulation...."

Michael,
Despite the sayings of Donald Rumsfeld, et al, "degrade" is not necessaryly a synonym of "reduce." It can also mean "damage." This claim as you have restated it could be taken to mean only that moisture from the breath does not cause "DEGRADATION" of the insulation in the sense that it does not damage it.
It's an issue of semantics, obviously mastered by a company with megaprofits.

Anyone who has worn a moist T-shirt in chilly weather knows that moisture reduces insulative value. The only question is, how much. More, say, than could be ountered by putting a welded heatsheets type space blanket sleeve around the pad? Would the sleeve be lighter and/or more convenient than hauling a pump? Could a small filter sleeve remove most moisture from the breath for blowing a pad up?

There was a thread in which Roger Caffin talked about hanging his sleeping pads valve end down with the valves opened between trips. He also did an article on air mats, and has done a lot of work on measuring insulative values. Maybe he will have time to post on this issue in this thread. If not, maybe someone will dig out the link to the older thread.

I prefer the foam filled inflatable mats, but the same issues appear to apply there also.

Edited by scfhome on 02/01/2013 21:37:48 MST.

moist teeshirt in cold weather - water evaporates from shirt which takes heat, so it cools you down - evaporated water goes into atmosphere

same as canister in upright stove cools

inside a mat, there's no evaporation - it's enclosed - evaporated water doesn't go away into atmosphere - won't have evaporative cooling

"Anyone who has worn a moist T-shirt in chilly weather knows that moisture reduces insulative value."

Here there are two mechanisms for heat loss -
Evaporative, the heat loss occurring when a liquid converts into a gas, and
Conductive, when the water in the soaked insulator facilitates the movement of heat from high to low

Jerry, you are choosing evaporation when you say -

"inside a mat, there's no evaporation - it's enclosed - evaporated water doesn't go away into atmosphere - won't have evaporative cooling"

But be careful...

The upright canister is cooled as liquid goes to vapor. Even thought there is a throttled fuel line that precipitates the pressure drop, the canister per se is a closed system, like an air matt. And it is absorbing heat via direct contact with a "warm body" - the atmosphere in this case.

Water will suck up 540 calories per gram to vaporize. So if one were to Really split hairs, there Could be a heat sink as you cook the interior water liquid into vapor. That heat is still in your pad, but you only get it back when the gas condenses.

Again, as mentioned above by myself and others, is it significant? For most of us, probably not. But it does make for an interesting first year physics discussion.

Edited by greg23 on 02/02/2013 07:28:31 MST.

With a canister, the gas leaves the canister, taking the heat with it, leaving the canister cold.

With a mat, it could evaporate, and the gas could condense against an outer surface, where the heat released would be quickly conducted away. But there is so little water in the mat. And it would happen early in the night, when your metabolism was higher so it wouldn't matter, and after that you'de just have a few beads of cold water sitting there not doing anything.

I wonderif anyone has weighed their neo-air after a few trips to see if it's gaining water weight.

Yeah, this is mainly just a first year physics problem, although if a mat accumulates water over time, that wouldn't be so good.

Edited by retiredjerry on 02/02/2013 07:56:29 MST.

I just got back from the coldest hike I have ever taken. (Well I "slept" colder once but this was the coldest while hiking.) It was -27 F at the town I went through 15 minutes from the trailhead so I figure it was probably -25 F as I started. It did not warm up much during the day and was -22 F last night. The cold killed my camera, I had to keep the battery in my pocket and still some of the pictures were whacked out. I had used batteries in my Microburst and the cold sucked them down by the time the pad was half-full. I had new batteries in my headlamp but did not want to mess with it as I would have to take my gloves off, so since it was just one night I inflated it the rest of the way by mouth.

After reading this thread I grabbed the pad which is still rolled up from the trip and weighed it. There is 4 g of extra weight so I will assume that is moisture. That's not bad really.

Good Ray

Did you dry off the outside of the pad? My pad will weigh 0.4 ounces (10 g) after a trip, then lose that weight after a few days.