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Jim W.
(jimqpublic) - MLife

Locale: So-Cal
Re: So one R-value is good for virtually all snow camping? on 04/26/2010 16:42:08 MDT Print View

Actually I agree "one R-value is good for virtually all snow camping". I just had a shocking reminder last weekend after forgetting that fact. In colder conditions the snow stays below freezing and provides some insulation. In warmer conditions the snow is probably icier and conducts heat more- but it isn't as cold.

The most important thing I want to emphasize is that an inflatable insulated air mattress provides comfortable padding because it compresses under your pressure points such as hips and shoulders. Unfortunately it also becomes cold at those points unless it's quite thick.

So my bottom line is either layer a closed-cell foam pad under your inflatable, or make sure the inflatable keeps you well off the snow.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Re: So one R-value is good for virtually all snow camping? on 04/26/2010 16:47:22 MDT Print View

On a related topic, I tended to see the highest failure rate in air valves and such when the temperature got the lowest. We all keep such systems tested for normal temperatures, but when it gets really cold and you need the insulation the most, that is when the failures occur most. As a result, for snow camping purposes, I never rely on an air-filled anything for more than 50% of my sleeping pad. Quite commonly, I will have one Thermarest plus one CCF pad.

--B.G.--

Robert Blean
(blean) - MLife

Locale: San Jose -- too far from Sierras
Re: Re: So one R-value is good for virtually all snow camping? on 04/26/2010 19:39:28 MDT Print View

No, I don't believe so. I think you are over-simplifying snow temperatures. In some places surface snow is affected more by air temperatures, and in other places, surface snow is affected more by deep snow temperatures.

Bob,

Are you sure? Since properly packed snow (i.e. not overly compressed) is a pretty good insulator, I would expect the snow under you to soon come to some equilibrium temperature, and then not transmit an awful lot of heat.

This is assuming that you are not camping on ice, or hard-packed snow (such as boot-packed).

--MV

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Re: So one R-value is good for virtually all snow camping? on 04/26/2010 20:08:35 MDT Print View

Bob B., I don't know what part of California it is where you snowcamp, but I've been all over. The only generalization that I can make about California snow is that I can't make any generalizations about it. Often, we do boot-pack or ski-pack the snow before setting up a tent or digging a snow cave. Yes, I would expect the snow directly underneath your sleeping pad to arrive at some equilibrium temperature, but that temperature is fairly unpredictable. You might have cold snow below and soft ice cream on top, or vice-versa. You don't know whether the water will be rising upward or sinking downward. We camped in Yosemite one time, and all of a sudden in the middle of the night, I started hearing noises and feeling collapse underneath me, and my sleeping bag and pad dropped about an inch. It was shallow depth hoar that had collapsed.
--B.G.--

Brad Groves
(4quietwoods) - MLife

Locale: Michigan
Re: re Brad on 04/27/2010 11:13:18 MDT Print View

Andrew, most of your comments mirror my own, so I guess most of your thoughts are also misinformation?

One thing that you're right about is that the baffles do contribute--even significantly--to the warmth of the pad. However, your statement "the fact that the baffles are reflective is a minor enhancement" is patently incorrect, because the baffles are not reflective. For those curious, the radiant heat barrier of the NeoAir only accounts for approximately 25% of the R-value of the pad. Cascade tested the pad as just the shell w/the baffles, no radiant barrier, and found an R close to 2. I was quite surprised to learn that. My personal feeling is that the baffles do a lousy job controlling convective current transversely. Apparently that is some concern, & although entering the realm of "hard to tell," a Cascade employee has concurred w/my previously expressed thoughts that you do have some extra heat loss thru the sides... but which can be mitigated by use of a tent or a narrower pad with a sleeping bag that overhangs the edges of the pad to keep the heat in. My problems occurred w/a wide pad and a narrow bag under a tarp.

Please note that your comment "Yes, they keep you warmer when formed into a bag because they then trap air. They are also a vapour barrier so stop evaporative heat loss." echos exactly some of my comments.

On "This is not possible unless the blanket was formed into a multilayer corrugated blanket like a Blizzard Pack, in which case it is again trapping air," re: the R-value, apparently some testing has found that it is possible. If I recall correctly, however, those tests were done in a different context, that of building materials & construction. If I can find the references, as I stated originally, I will post them. I have owned and used a blizzard bag (actually MPI) and it is quite remarkable. But it is a different matter.

"Only if you've already reduced the other sources of heat loss to a minimum," Um... Yeahhhh. That falls into the category of "Duh."

I do appreciate folks comments about the baffles, because it made me do some more research and I found that they do contribute more significantly to the insulative value of the pad than I originally thought. Ie, I was wrong about the radiant barrier being the primary warmth. I've had one the pads cut apart in my hands, investigating it closely, and could not discern any practical R-value in the baffling. Just goes to show ya!

Cheers, all-

Andrew Dolman
(andydolman) - M
Radiant Barrier on 04/28/2010 02:06:24 MDT Print View

So did the prototype without the radiant barrier still have a non-radiant barrier suspended between the two layers of baffles? If so I stand corrected, and surprised, at the 25%.

bill smith
(speedemon105) - F
Radiant energy loss on 04/28/2010 09:46:59 MDT Print View

I think alot of people here are using anecdotal evidence and dismissing space blankets altogether. While they are not ideal, and they don't stop other forms of heat loss, the amount of heat they can conserve is not insignificant. Depending on the difference between skin temperature and the outside temperature, you can be losing several hundred watts of energy through IR radiation.

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/bodrad.html
Play around with it some.

James Klein
(jnklein21) - M

Locale: Southeast
misinformation on 04/28/2010 12:03:22 MDT Print View

Actually, most of the anecdotal evidence I have noticed seems to support space blankets. Most of the misinformation I have seen comes from inappropraite application of theory (ie it appears to be "knowledge" based not experience based).
I few points for those still following this:
>As Bill's link shows - heat loss via radiation xfer IS significant, even at 3season temperatures.
>Space blankets don't need an air gap to be effective at blocking IR radiation. Distance btw surfaces has NO effect on radiation heat xfer.
>Assigning an eqivalent R-value to a space blanket is almost useless as it will only apply to the temperatures it was tested at -- the same applies to assigning a % of insulating value.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: misinformation on 04/28/2010 18:51:57 MDT Print View

Guys

We have a review of the Neo-Air on the site. If you go through it you will find out more about the use of radiant barriers. They do something, but under many conditions 'not very much'.

A Space Blanket does most of its 'good' by limiting wind chill and stopping evaporative loss. The radiant barrier in it is often rather irrelevant. Try using a very large trash bag instead.

Cheers

James Klein
(jnklein21) - M

Locale: Southeast
re:re:misinformation on 04/28/2010 19:59:54 MDT Print View

Roger, for some reason I've never notived that acticle. Pretty good review though I would like to know where you guys came up with the radiation claims.

>>"The amount of heat radiated from the body is small compared to typical convection losses, especially at colder temperatures"
--while I could come up with some scenarios where this is true, I don't think it is typical. Also, the colder it gets the more significant IR heat xfer becomes relative to other modes of heat loss (its a fcn of T^4).

>>"...and the pad only intercepts a fraction of this radiated heat"
--A small fraction is "intercepted" (ie absorbed) and a larger fraction would be reflected back to you, though I don't think thats what you meant when you used intercepted.

>>"any intervening clothing and fabric ... will already block some of this infrared radiation"
--This is true so long as "some" is emphasized. Most all fabric is nearly black to infrared radiation (emissivity ~ .8-.9). So only a small portion of you heat is reflected back by these

>>"Third, placing a radiation shield within the pad will only halve the amount of radiative heat loss"
I guess what you mean here is only half b/c its only below you?. If so that similiar to saying the down in a DAM is gimmicky b/c it only blocks some of the convection losses.

Finally in responce to your post in this thread:
Space blankets do help with wind chill and evaporative losses but they (unlike a garbage bag) will also significantly reduce radiative heat transfer. In MANY conditions this can be the a very significant heat loss mechanism.

looking forward to discussion,
James

bill smith
(speedemon105) - F
Re: Re: misinformation on 04/28/2010 21:04:43 MDT Print View

"A Space Blanket does most of its 'good' by limiting wind chill and stopping evaporative loss. The radiant barrier in it is often rather irrelevant. Try using a very large trash bag instead."

Why use a trash bag instead, when a space blanket will do more? Im sorry, but I don't see stopping the loss of hundreds of watts of heat as irrelevant.
Your attitude is my point exactly. Because it isn't a do-all insulation, it should be discarded as worthless.

Jason Elsworth
(jephoto) - M

Locale: New Zealand
Radiant barrier, R values etc on 04/28/2010 22:32:15 MDT Print View

Almost 30 years ago now I had a Mountain Equipment synthetic bag with a silver radiant barrier in it. The concept didn't seem to catch on widely, but I did find this online http://www.livefortheoutdoors.com/Gear-Reviews/Search-Results/Sleeping-bags/Mountain-Equipment-Mithril-II-/. They claim it adds 3 degrees to the bag.

Going back to pad R values and the Neoair. Eddy Meechan wrote an article in TGO magazine a few months ago where he suggested that the Neoair's R value would to some extent be dependent on the amount of air you have in it. The more air the higher the R value. Most people seem to use their Neoairs some way from fully inflated. Whereas the cynic in me says that the lab test to determine the Neoairs R value may have been done at full inflation :).

In his article he also points out that there is no standardised R value test that pad makers use, so comapring the R values between the pads of different makers may be a bit suspect. He also argues that R values in the lab and those in the field may vary cosniderably. He concludes that R values are probably of most use in comparing mats of the same construction type by the same manufacture.

George Geist
(geist) - M

Locale: Smoky Mountains
Re: misinformation on 04/28/2010 23:59:52 MDT Print View

> Depending on the difference between skin temperature
> and the outside temperature, you can be losing several
> hundred watts of energy through IR radiation.

Indeed a Space Blanket's IR barrier can cut a significant loss of heat, especially when placed over the body between your 98 degree body and the near absolute zero degree night sky. But even in less extreme temperature differences the T^4 in the IR radiation loss equation can account for hundreds of watts lost just as Bill says.

Edited by geist on 04/29/2010 00:01:20 MDT.

Stuart Allie
(stuart.allie)

Locale: Australia
Re: Re: misinformation on 04/29/2010 00:28:49 MDT Print View

Um, "the near absolute zero degree night sky?" I don't think so. If there was no atmosphere between you and the sky, you'd be right, but then you'd have bigger issues :)

Don't forget that the atmosphere is also radiating in all directions based on its temperature. It's the difference between your body temperature and the ambient air temp that matters; the temperature of outer space really doesn't come into it.

Franco Darioli
(Franco) - M

Locale: Melbourne
Neoair vs. Space Blanket on 04/29/2010 01:09:08 MDT Print View

"Going back to pad R values and the Neoair. Eddy Meechan wrote an article in TGO magazine a few months ago where he suggested that the Neoair's R value would to some extent be dependent on the amount of air you have in it"

Oddly the review at Backpackinglight (....) came to the same conclusion.
http://www.backpackinglight.com/cgi-bin/backpackinglight/thermarest_neoair_review.html
Franco

Jason Elsworth
(jephoto) - M

Locale: New Zealand
Neoair on 04/29/2010 01:19:18 MDT Print View

Oddly the review at Backpackinglight (....) came to the same conclusion.

This could go some way to explaining why some users seem to sleep very cold on a Neoair and some seem to do fine? Obviously many other factors will come into play. However, I would suggest that the amount of air in the mat may have less of an impact in the traditional foam and air pads than with the air only pads like the Neoair.

Franco Darioli
(Franco) - M

Locale: Melbourne
Neoair vs. Space Blanket on 04/29/2010 01:45:26 MDT Print View

My impression is that "perception" comes very much into it.
For example I have a mate that happens to be very experienced in tenting in cold weather,( and I mean -30-40f air temperature), yet he firmly believes that sleeping naked he is warmer than wearing a base layer(not a compression layer).
Now since he is "sure" of that, it works for him, does not work for me though.
Franco

Stephen Klassen
(SteveYK)
Conduction greater than radiation when on snow on 04/29/2010 02:56:52 MDT Print View

Hi Adan,

My experience with sleeping on snow (air temps from +12C during an inversion down to -23C) is as follows:

R3.5 left me cold. Not at the beginning of the evening, but early in the morning when metabolism slows. (Montbell pad or Prolite 3 with GG 3/8" thinlight.)

R5.3 and I slept warm the full night. (Thermarest Toughskin).

My bag was a Marmot Aiguille (O F degree rating) and I used either a sylnylon VBL from FF, or a WM Hotsac (which has a reflective coating on the inside).

With regards to reflective coatings, I found that I could not use the WM Hotsac - too much moisture buildup in the VBL. I have used my FF silnylon VBL extensively and never had such moisture buildup. I only use the VBL at below freezing temps (except one time when I used the Hotsac as an emergency blanket in the low 40's F- very warm, and very wet).

When we snowcamp, we always lay a reflective space blanket under the tent. It only covers about 2/3 the floor area, and we always know exactly where it has been once we pack everything up - the compacted snow outside the area of the space blanket is very icy, while the snow that was under the space blanket is merely compacted, not icy. Needless to say, I always try to get in the middle of the (3-person) tent.

Anyay, back to conduction and radiation. I was getting cold feet (literally) and decided to augment my booties. They came with 3/8" of closed cell foam (approx R1.3?). I added cutouts that were about 5/8" (additional R1.7ish? for total of R3ish?). Feet were no longer cold.

Then, one trip my skiing partner had cold feet. His booties had seen extensive use, and the synthetic insulation had long since collapsed. He didn't have the extra layer of foam. So we started to swap booty parts. We tried my lofty booties with and without the extra foam, and compared them to his saggy booties with and without the extra foam. What we found was that his saggy booty with extra foam was warmer than my lofty booty without the extra foam, and we really couldn't tell the difference between the booties if they both had extra foam.

To make a long story short, after that night I decided to ditch the R3.5 pad/-10F bag system and went with the R5.3pad/+20F synthetic bag and clothes for winter camping. And now I don't wake up cold in the early hours.

Edited by SteveYK on 04/29/2010 02:59:15 MDT.

Andrew Dolman
(andydolman) - M
relevant to our interests on 04/29/2010 03:02:14 MDT Print View

http://www.backpackinglight.com/cgi-bin/backpackinglight/00184.html

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: misinformation on 04/29/2010 04:48:48 MDT Print View

> between your 98 degree body and the near absolute zero degree night sky.
Sorry, but that is wrong.
The night sky on a nice clear night is about -70 C from memory. Stick any high-level haze in the way and the temperature climbs.

> in less extreme temperature differences the T^4 in the IR radiation loss equation
> can account for hundreds of watts lost
Bit hard to imagine, since a resting body puts out about 60 W from memory.

Cheers