Apr 26, 2011 at 11:40 am #1272894
@dtpaladinoLocale: Northern Rockies
Companion forum thread to:Apr 26, 2011 at 11:59 am #1729702
@clbowdenLocale: Berkeley Hills
mm to inch conversion for the last figure
44 mm = 1.73 in
29 mm = 1.14 in
18.5 mm = 0.73 in
14 mm = 0.55 inApr 26, 2011 at 2:37 pm #1729754
Thank you so much for putting together this seminal article. For us backpacking nerds, this is fascinating. I am eager to see what comes next.
It is also another reason why BPL is the leader in the field.Apr 26, 2011 at 3:22 pm #1729771
@hikinggrannyLocale: Gateway to Columbia River Gorge
The article was simple enough that I understood it! Having been "skunked," or rather frozen, by several pads over the years, I would really like to see some standardization–hopefully your work will bear fruit in the future. Thank you, Roger, for your work and the excellent article!Apr 26, 2011 at 4:18 pm #1729800
This article goes a long way towards justifying my recent subscription renewal. I'm certain the follow test reports will complete that task.
Nice work Roger.Apr 26, 2011 at 4:25 pm #1729804
@davecLocale: Crown of the Continent
Quite digestable for something like me with minimal hard science background.
I look forward to the empirical findings.Apr 26, 2011 at 4:34 pm #1729807
@brendansLocale: Fruita CO
Definitely looking forward to more. Even the findings here with the pad thickness are pretty interesting considering that many neoair/other inflatable users don't fully inflate the pad for more comfort.Apr 26, 2011 at 5:38 pm #1729840
Superb text and pictures. Your explanations are great. Thanks for your continuing service excellence!Apr 26, 2011 at 6:19 pm #1729852
@daviddrakeLocale: North Idaho
Excellent introduction–looking forward to more.
Roger, are you saying the listed r-value on sleeping pads (eg, 1" thermarest prolite 3, stated R-value 2.2) is based on SI units? Versus building insulation products in the US that use imperial units (eg, 1" of EPS foam board ~ r-value 5.0)? You say SI units gives an r-value about 6X less than imperial units. Does this mean sleeping pads are actually much better insulators per unit thickness than common building insulation (eg, 1" thermarest prolite would be equal to R 13 in terms of US building insulation)?
Sorry, I'm a bit confused.Apr 26, 2011 at 6:42 pm #1729859
aApr 26, 2011 at 8:17 pm #1729893
Daryl and DarylParticipant
@lyrad1Locale: Pacific Northwest, USA, Earth
This is just plain wonderful! I have sought this info for decades. I don't have an engineering degree and most info I have seen in the past only confused and frustrated me. I can actually understand most of what you wrote here. Empirical work in this area should help to separate myth from reality.
Here are a couple of questions I've had relative to this subject:
How much blue foam would be required to roughly equal the insulating value of 2" of down?
What's a common sense guideline for comparing sewn-threw construction in a down sleeping bag compared to box or overlapping tube construction? For example, would 1.5 " of down which is sewn through be warmer than, say, 1" of down within a box constuction?
DarylApr 26, 2011 at 8:54 pm #1729917
@biointegraLocale: Puget Sound
A fantastic teaser… looking forward to the data sets. BTW, great work, Roger. :)Apr 27, 2011 at 1:59 am #1729989
> listed r-value on sleeping pads (eg, 1" thermarest prolite 3, stated R-value 2.2) is based
> on SI units? Versus building insulation products in the US that use imperial units
> sleeping pads are much better insulators per unit thickness than common building insulation
Correct, along with all that implies.
CheersApr 27, 2011 at 3:13 am #1729992
> how the end effects are accounted.
Bluntly, they aren't.
But in the field the conditions are highly variable, so attempting to measure R-values of airmats to any high level of precision is both meaningless and futile.
> I assume you will strive to have ambient conditions similar for all tests.
Yes. Can't be exact (see above), but yes.
CheersApr 27, 2011 at 3:16 am #1729993
> How much blue foam would be required to roughly equal the insulating value of 2" of down?
Um … I think Richard Nisley might have better figures for that than me.
> would 1.5 " of down which is sewn through be warmer than, 1" of down within a box construction?
Another Q for Richard. As sewn-through constructions are rather more variable in performance, that could be very hard to answer.
cheersApr 27, 2011 at 7:56 am #1730039
@jamesdmarcoLocale: Finger Lakes
Great work, Roger! Looking forward to the airmat survey.Apr 27, 2011 at 11:15 am #1730126
The "edge effect" sounds like a tough problem to handle. Basically, as I see it, you could lose heat in three areas. The first is right where you are measuring (the bottom). The second is on the sides and the third is on top (but through the mat first). The same is true out in the field. The heat can transfer into the pad, then out to the sides, or back up to the top in the section of your pad that isn't covered by a sleeping bag/quilt. Solving the problem with the sides of the mat seems easy — just let it happen. If a pad loses some heat to the sides during testing, then it will lose some heat in the real world (unless the camper insulates the edges). Solving the loss to the top of the mat sounds harder. In the real world, part of the sleeping bag/quilt covers it up. But depending on the shape of the mat and the sleeping bag/quilt, some of it is uncovered. To get a good estimation, you might want to measure things with various coverings. Start by laying a good bag over the rest of the mat, then cover only part of it, then cover none of it.
It would be interesting to see how mat combinations work under these conditions as well. As has been reported by many people, if you have an inflatable and a closed cell mat, you are better off putting the closed cell on top. Without the edge effect, I would assume that it would make no difference. I would be curious as to much of the loss is due to the sides of the mat, as opposed to the uncovered top.Apr 27, 2011 at 5:38 pm #1730249
@fluffinreach-comLocale: no. california
a very long time ago in high school, al (a genius) and peter (not quite a genius…) decided that while stuck in experimental filmaking class with the hippie chicks, that we should determine a formula that once the data was entered would tell us (in advance you see. a leading indicator in todays lingo) if the girl was .. "any good".
this project turned out to be a failure for any number of unmentionable reasons, but i suspected from that day that hippie girls would end up being a lot like camping mats, in that in order to tell if it's a good one, you really need to sleep with it.
in the end, sleeping with them is going to be the best way.
a keeper ?
a tosser ?
it only takes a night or two to find out what you need to know.
but peter ! … you'd have to sleep with ALL the mats….
yes .. that might be a problem. i suppose that the mats that initially didn't look so hot, we could just pass around thru the group.Apr 28, 2011 at 7:36 am #1730440
Good Work Roger. Your always pushing the envelope.
LawsonApr 28, 2011 at 8:24 am #1730453
Roger, I am not an engineer, so frankly some of the more technical aspects of your article were a bit over my head. But the bottom line is that based on your previous work with BPL, I trust you. Therefore I welcome your new testing apparatus and look forward to future comparison tests.
Slainte! (Irish for CHEERS!!)Apr 28, 2011 at 2:48 pm #1730622
@nmanhipotLocale: North Georgia
Roger, thanks for the insight into your testing apparatus. Kudos on encouraging independent testing!
Question – you mention that you obtained a calibrated piece of insulation. What was it? Concerns – 1) Consistent ambient temperature. 2) Consistent coolant temperature. 3) Eddie currents and convective heat dissipation (as mentioned) in air-filled pads.
For pad to pad comparison, would it not do to put sand bags wrapped in an electric blanket evenly distributed inside of a sleeping bag on top of each pad and place an array of thermocouples above and below each pad? You could mount a set of six at 30 cm spacing along a 3 cm x 185 cm strip of thin lexan, for example, and align the strips vertically at their ends, effectively sandwiching the pad. Again, consistent ambient temperature would be the biggest variable, but this would allow a precise measurement of the temperature differential between the sensors above and below the pad. I haven't thought through how you would derive R value based on this differential, but this seemed closer to a real-world test to me.Apr 28, 2011 at 3:42 pm #1730639
@retiredjerryLocale: Oregon and Washington
I've been looking forward to this article, thanks
I will be interested in seeing R values of various pads and other stuffApr 28, 2011 at 6:17 pm #1730694
> calibrated piece of insulation. What was it?
EVA30 CCF foam
> 1) Consistent ambient temperature.
Controlled and measured hot and cold plates
> 2) Consistent coolant temperature
Huge water tank on house, plus continuous measurement.
> 3) Eddie currents and convective heat dissipation (as mentioned) in air-filled pads.
Limited compensation by wrapping the towel around the system as shown. But the stability is greater than you would get in the field anyhow!
> an array of thermocouples above and below each pad?
This is possible but messy. Using solid aluminium plates to even the temperature out is an accepted industry method, and works fine for this case. Then you only need to monitor the temperature of the Al plates in a few places. I found *from experiment* that monitoring at the centre was adequate.
Btw – thermocouples require expensive electronics and need calibration. They are fine for very high temperatures. For ambient conditions they have been largely replaced these days by either thermistors or semiconductor sensors. I use the latter.
CheersApr 28, 2011 at 7:44 pm #1730726
The benefit of your test is not the accuracy of R, but in the consistency of the measurement across all products. We await your unbiased results.Apr 28, 2011 at 11:10 pm #1730790
@dirk9827Locale: Pacific Northwest
Great article – kind of stuff you don't read anywhere else…
I would like to see tested the oft-discussed "double up" practice of 3-season air mattress coupled with a thin pad for extra warmth. I wonder how that compares to other solutions, particularly those 4-season pad with a purportedly higher R-value but at a cost of greater weight.
Finally, I do agree Peter, a pad that allows you to sleep well is the best pad out there….
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