Neoair and humidity in breath??!!! – a hoax?

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.

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.

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.

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.

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.

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.

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.

Well the reason I think these are different than Prolites or down/synmats is:
OF course in the lofty ones there is the degradation of loft due to humidity
in the prolites of the world – i assume the small cavities in the OCF might fill up with water vapor and then when it condenses or freezes they might be full of water or ice – of course this will not be ALL the cavities but it might over time fill quite a few.

With the neo airs – the size of the cavity is so large that i tend to agree the chances of conductive heat transfer are slim.
RE evaporative – I assume since its a closed system once the systems stabilizes as vapor pressure goes up water will stop evaporating.

I guess my concern is over a longer trek (say 10 days) how bad can this get…
4 grams doesnt sound so bad but then its 1% of weight….hmmmm for 1 night…..

RE long term – well I guess if there is one thing CD is looking at technology wise its that…so i tend to rust them on that.
Also – I live in a warm country so i know my stuff will dry at home pretty well

Maybe worth writing in to CD to ask?

It was dry Jerry. I was not directly on the pad this time as I was using a bag and over-quilt combo.

But just about everything else had frost on it that my breath vapor touched. Ha, my eyelashes froze together as I was hiking!

Well, their claim is not a HOAX, although it may not be entirely accurate in practice. We need to distinguish between 'air' mats, mats with insulation inside, and the NeoAir mats. To explain:

Blowing up a mat with your mouth puts water vapour inside the mat. We know that. What happens to the water depends to some degree on what sort of mat it is.

If the mat is full of internal insulation – eg a DAM, then the insulation can get damp and lose some of its insulation properties. However, see the next bit before drawing any conclusions here.

In the case of an 'air' mat, it is likely that the few grams of water will collect at the bottom of the mat and in really cold weather it will freeze there. The water won't collect at the top where it is warmed by you. In effect, it's a bit like a old refrigerator where all the ice collects on the surface of the freezer rather than all through the rest of the chamber: it goes to where it's coldest.

Now a thin layer of ice on the inside surface of the bottom layer of fabric in an 'air' mat is not very different from a thin layer of ice on the outside of the bottom fabric surface. We may be talking about a small area of ice only 1 mm thick perhaps, on the fabric. That is not going to have much effect on the overall performance: all the rest of the air space is still there. So there won't be a big change in the R value. That is, unless you really thrash around in the night and stir the air up – which is where all 'air' mats fail in the cold.

Coming back to the DAM, the same thing applies: the ice will mainly collect at the bottom surface. In this case, a bit of thrashing around won't have as much effect. So the loss in the R value of the insulation should not be too high in practice.

Where does the NeoAir fit in all this? Well, it is really just a complex multi-layer 'air' mat, so the water should still collect on the ground surface (ie at the bottom). Provided you drain the mat out when you get home, there should be no long-term effects on the obvious insulation value. So far, so good.

But the aluminised coating on the internal baffles is another matter. In theory the water should have no effect on it, but field experience suggests that the coating on the early models was not good. It rubbed off. People experienced this. Mind you, I am not sure whether the aluminised layer really did much for the R-value anyhow. Regardless, I have to say that water inside the NeoAir mats did seem to cause some degradation on the early models. I don't know about the more recent models after CD tackled that problem. I would expect that CD would have largely solved it: they are fairly competent.

Anyhow, I think CD was willing to replace mats where there was a major problem – they are good that way.

My 2c.
Cheers

They've tackled at least one "problem"… I bought a xlite a couple of weeks ago and it hasn't the see through material found on earlier xlites. If I recall the original neoair right I'd say my xlite has a similar somewhat sticky non see through shell as that.
In other words, no visible delamination of the aluminium, no complaints?