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Does anyone know of a reasonably simple means of using household items to objectively measure the insulating value of a sleeping pad, in a way that accurately predicts that aspect of performance in the field?

I would imagine that this would involve creating some of the field conditions (for example compressing the sleeping pad by a realistic amount)—-what would those conditions be?

This could be valuable either if it was able to produce absolute measurements (assigning an R-value under a certain set of conditions that would be the same as one measured by a manufacturer’s lab) or only relative measurements (Pad A is about twice as good as Pad B)

My goal here is to contribute to actual comfort and safety in the field. I’d like to devise something either so simple people could test their own setup, or if not, then to enable some individual who is so inclined to measure a bunch of common gear and post results. This is motivated both by appreciation for truly well made commercial products which deserve recognition, but also spotting where very cheap alternatives attain the basic safety and function.

  • I’m wondering what could be done with (for example) a bag of ice, a pot of water, a thermometer and a watch, in a basement of consistent and known temperature. – mmcc Sep 2 '18 at 16:55
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If you want to test a sleeping pad's insulation yourself at home, then the way to do that would be to try sleeping outside your house in and see how they work. That is worth doing because you might sleep differently from the next person.

On the other hand, it seems like there is no simple way to retest for the R-value assigned by the manufacturer as that requires equipment.

See how Thermarest measures the R-value of their pads.

Technically, R-value is a measure of thermal resistance; the higher the R-value, the more thermally resistant the material or structure is. This isn’t just used to measure sleeping pads. It’s used by engineers and scientists to measure everything from windows to fiberglass. Our team believes that it’s also the best way to measure the insulation of our pads.

We measure every mattress design in our on-site cold chamber, kept at a cool 4C (39F). Inside this thermally-sealed container, a mattress is placed between two metal plates. A section of the bottom plate has been turned into a large sensor and is kept at a steady temperature with a measured electrical current. A mattress that provides a lot of insulation will help keep the bottom plate warm and, as a result, the sensor will require less electricity (energy) to maintain its temperature.

R-value: The meaning behind the number

A sleeping pad's R-value measures its capacity to resist (hence the "R") heat flow. The higher a pad’s R-value, the better you can expect it to insulate you from cold surfaces. The R-values shown on REI.com product pages are provided by the manufacturers and range from 1.0 (minimally insulated) on up to values of 11.0 or more (very well insulated).

How to Choose Sleeping Pads

Do note that there is not an agreed upon standard of how to measure the R-value,

Currently there is no standardised method of testing R values which means each brand might have their own method of testing which yields its own results. These results can be misleading, and as customers this makes it hard to compare mats manufactured by different brands.

Why don’t we use R values?

and some use temperature ranges instead.

Some manufacturers, like Big Agnes and NEMO, don’t use R-values. They opt instead to simply specify a temperature range their pads are suited for.

How to choose a sleeping pad.

  • this is very helpful especially the piece about the lack of cross-industry testing standards. This makes me feel a comparative A:B test may be the best that can be hoped for. This might be an example of a situation in which industry incentives are not aligned perfectly with customer incentives—Thermarest has no interest in showing the cheap foam is pretty good, and the makers of cheap foam have no budget for testing. – mmcc Sep 2 '18 at 16:04
  • Also I think it’s very true that different bodies compress pads differently: fat/skinny, side sleeper/back sleeper, bulky clothes or no. There’s no substitute for a field test but that requires multiple nights to have value. I think a bench test could at least identify the good options. – mmcc Sep 2 '18 at 16:15
  • A somewhat interesting point is that sleeping bags use temperature ratings instead of R values – JollyJoker Sep 3 '18 at 8:22
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It is not clear whether you are motivated mainly by scientific curiosity or mainly by a desire to ensure comfort in the wild. My answer assumes the latter.

This answer adds only one point to Charlie's excellent answer, and refutes one of your reservations to his answer.

A stringent test as to whether your pad is good enough for all (or almost all) of the conditions you will encounter in the wild, is to spend a night outside on it in the snow. Of course, if you live in Florida, this is impractical.

But if you can camp out on your terrace or backyard in the snow, you will need only one night to "rate" your pad. Note that you may be adequately insulated from the snow, but that does not mean that the snow is adequately insulated from you. If you wake up and find yourself immobile, sunk into a shallow, icy grave, because the snow has melted and refrozen under you, your pad is not adequate for snow camping, but is probably adequate for anything down to about 15 to 20 degrees F.

Aside from a one-year fling with inflatable pads, we've used simple, inexpensive 3/4-length Ensolite pads and have been perfectly comfortable, even without a tent, in the high teens, except for one awful night on snow at four degrees F (in a tent).

  • your assumption is correct—comfort and to some extent safety – mmcc Sep 2 '18 at 17:11
  • Also I like the snow as a way to focus on the pad-ground interaction vs the air temperature etc, especially since melting snow is always the same temperature regardless of weather – mmcc Sep 3 '18 at 23:28
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Other than sleeping a night outside on it, there is no way to test whether it will be comfortable in the wild for you, however...

A simple test for its insulating properties would be to get 3 1 litre/gallon jugs, leave one cool, and allow it to adjust to ambient temperature, then heat up Two 1 litre/gallon jugs (amount doesn't matter so long as they are all the same). its important to not have boiling water as anything over about 60 degrees C has a chance of damaging the roll mat

Take the roll mat and wrap it round on of the heated jugs once, any excess length do not wrap it round again, you should secure it away from the jug. and pop a thermometer in each, and leave the other unwrapped

Then leave them alone, checking back every half hour or so, the expose water is your control so you can see how quickly the water will cool without the insulation and then you can see how quickly the insulated one will cool.

the amount of time it takes to cool down reflects how insulating the matt will be

be advised though the "truest" way to test it would actually be to not wrap the jug at all, instead leave both jugs on the ground with the mat under just one as the jug would be you in real life. but this would men that the temperature would change much more similarly so you may not feel reassured.

Then take several different mats and re-run the test, and then if you do it with enough mats you'll have a decent basis to go on in order to compare them.

This test is only for your reassurance, any roll mat underneath you so long as it is waterproof, is a lot better than none. but as other have already suggested the only true test is to sleep outside on it.

Of course if you have all that data... then you may as well publish it, then continue doing so and become a camping mat tester blogger. but you're overheads on shipping, items, water bill and electric bill to heat up that water might be prohibitive...

  • Yeah this is the kind of thing I was imagining. Either letting something warm cool, or letting something frozen melt. Could make the experiment and see if it can distinguish between say 1 mat and 2 mats. Hoping someone out there has already done the work! – mmcc Sep 3 '18 at 18:53
  • @mmcc, its unlikely they would have. most people just buy one and out they go. people who are going camping in Alaska in the winter tend to to have some experience camping and know what works for them. or people just find the one with the biggest or lowest number and trust that it will work... basically if you want the data, for the most part only the manufacturers will have it. – Blade Wraith Sep 4 '18 at 11:27
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    Yeah there’s probably like 3 people in the world who might get curious enough to do such a thing, but 2 of them might occasionally be on this site! – mmcc Sep 4 '18 at 12:48
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Simulate the setup as follows:

  • Use several 1 gallon milk jugs as your 'person' In the middle jug, put a hole in the cap, and insert a temperature probe. (Many multi-meters come with a temperature probe too.)

  • Fill the jugs with hot water.

  • Lay your sleeping bag on the mat.

  • Put the jugs in the sleeping bag and zip up the bag. Bunch the bag up close to the jugs to reduce convection effects.

  • Record the temp inside and outside the sleeping bag every X minutes (1/4 to 1 hour)

  • On a spreadsheet enter the inside and outside temps. Calculate a third column that is the difference between inside and outside. Calculate a 4th column that is the drop in temp during the interval.

Overall the drop in temp / difference in temp should be close to constant.

The notion here is that the jugs will compress the pad to a similar degree as you would, the sleeping bag insulates the tops of the jugs much as the sleeping bag would insulate you.

Repeat this several times for each pad.

  • 1
    I would also start with water at the same temperature each time. Maybe around 100C (body temp being 98.6) – James Jenkins Sep 10 '18 at 17:25
  • Thanks! Hey I wonder if one bottle would be enough (assuming the pad is same thickness everywhere) and if we could exaggerate the effect by placing it directly on a standard size brownie pan / paint tray filled with water and frozen to make a flat slab just a bit larger than the jugs. I like milk jug idea because the walls are so thin they would not insulate much. – mmcc Sep 11 '18 at 0:13
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If you want to see how good the pad itself insulates, then try sleeping in cooler/cold weather (snow not needed) where air can circulate beneath you. The open bed of a full size pickup truck works.

If the pad doesn't insulate well, then you should/will feel the cold steel. The sleeping bag beneath you will be compressed, yielding precious few insulative air cavities, so warmth under you is due the pad, not the bag (always better to be on the ground in cool/cold temperatures...)

  • I like this alternative method. it’s a sleep test but the truck bed offers a way to kind of amplify the effect of the pad vs all the other things going on. – mmcc Sep 3 '18 at 23:26
  • You're going to get edge effects -- one jug is a small heat source for a large sleeping bag volume. Most people have several milk jugs kicking around waiting to go back to the recycler, so it's not much harder to do with 3-4 than with one. Try it both ways and report back! – Sherwood Botsford Sep 11 '18 at 12:49

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