Another attempt to standardize r-values of sleeping pads

[Nick G]

This was born from Kevin Burton's post a few weeks back, which included a spreadsheet that compared the raw r-values and weights of various sleeping pads. Most pads can be cut down or bought in a smaller size to save weight, so comparing raw weights to R-values doesn't really help decide which pad is the best to use. This got me thinking, so I took his spreadsheet and added a few pads but mostly another comparison–I factored in the dimensions of the sleeping pad, allowing for a more accurate description of the value of each material. Because most pads are the same size, this doesn't affect most pads, but without it some pads would gain an advantage over others simply by being smaller, shorter, more narrow, etc.

Basically, where 'weight' was on Kevin's spreadsheet, I added "area density"–a calculation of the number of grams in each square centimeter of pad area. Then, I calculated what the R-value of a "standard pad" would be, using the average weight and standard pad size. This came out to 500 g (about 1.1 lbs) and 184×54 cm (about 74"x20"). Essentially, column D is a raw, abstract number which standardizes all the data (and has complicated units), and column C simply converts that into a number we're familiar with, which is R-value.

I'll comment on the top pads of this list when I have more time. For now, here's the spreadsheet. I encourage you to download it and modify it to fit your own needs (as I did with Kevin's spreadsheet). I'm also going to keep this up to date with any new pads which come along, as well as any that people would like me to add. All I need is data.

https://docs.google.com/spreadsheet/ccc?key=0AoQR5Mz_cmEudGlZcW1hNUg0OHd2ZGZmSWdOT2lvd1E#gid=0

There are several factors which are still not, and cannot, be factored into this. The primary one is comfort, but I also take packed size very seriously–that's why I use the Klymit X-lite in summer.

Another thing to keep in mind is that I'm not sure how much value you get out of an R-value much greater than 5–do the increasing R-values keep improving sleep comfort or is there a point where it is no longer worth it?

Note: as mentioned above, most of the data was collected and produced by Kevin. My own modifications are simply one step further to flesh out the information provided here.

[Tom Lyons]

Thanks for expanding the data base and adding criteria.

I am going to address the "problem child" for all these comparisons, which we all know is the Klymit pad. It defies comparison on the normal scales.

These are the reasons:

#1) We have test data that the "loft pockets" actually DO show R-value results higher than the body of the pad, and the company designed this into the system and patented it, which shows that they know about it. Since we don't see this in other pads, that makes comparisons difficult. The loft pockets showed R2.8, while the main body of the pad showed between R2.0 and R2.2, depending on how much it was pumped up. Adding the loft of the sleeping bag down insulation material in these Loft Pockets has, as yet, an undetermined additional benefit of insulation under the user, which permits the recovery of some of the sleeping bag lofting ability which otherwise is not seen at all in competing pads.

#2) The Klymit pads have a unique construction which permits them to be used INSIDE the sleeping bag. When the pad is inside the sleeping bag, it is not subjected to the outside air temperatures, or even the direct contact with the ground. This nearly eliminates convective losses, and reduces conductive losses to the ground enough to be significant. The pad operates in the heated environment of the sleeping bag, which sets it apart from all others. Other pads do not offer this option, and therefore they are all subject to serious losses in insulation performance from convection and conduction. This has the potential to GREATLY improve the cold weather performance of the pad, above and beyond any R-value rating that may be taken out of context with the pad in a stand-alone test.
And using the pad inside the bag prevents the pad from slipping out from under the bag when the user moves around. If the pad slips out from under the user with a normal pad, it could end up not being under the user at all, giving a zero R-value until the user wakes up freezing cold.

#3)When the pad is used OUTSIDE the sleeping bag, as some wish to do, it has a thinner profile exposed to the outside air, and therefore has less issue with convection losses occurring from air movement inside the pad body tubes. Thicker pads suffer more from convective losses from this air movement. Conduction losses to the outside air may also be reduced by the smaller wall area exposed to the cold outside air. However, the NeoAir pads 'may' suffer less than normal design pads from convective losses due to their internal baffle structure, and it would seem to be evident from their thermal performance rating in the new line-up. The baffles in the NeoAir perform the function of the thinner tube profile in terms of reducing convection losses by controlling unwanted air movement.

#4) The thinner profile of the Klymit pads is not necessarily "anti-comfort" as perceived by some. The Klymit pads are heavy-duty construction and can be pumped-up harder than other pads can. This gives a firmer base that 'might' be preferable to some, and could offer lower likelihood of "bottoming out" on the ground than might first be suspected from the thinner profile. At a lesser-than-full pump, the Klymit pads still offer a good comfort level(by my own personal test), which is surprisingly good for their thin profile.

#5) On the potential negative side, the Klymit pads are dependent on body size and shape fitting into their expected range for best use of this pad. This is a deal-breaker for those who do not fit, and there is nothing they can really do about it, even if they wanted to use the Klymit pad.
Another negative pointed out in the BPL test is that water in the floor or on the groundsheet can contact the sleeping bag material if the water intrusion moves to anywhere in the skeletonized areas of the Klymit pad.

#6) The flip side of #5 is that the Klymit pads are the lightest inflatable pads on the market for their respective sizes, and the skeletonized structure and body-mapping are part of what permit the light weight to be realized.

#7) As you mentioned, the Klymit pad(particularly the X-Lite) packs very very small, and I don't know of any other pad that can compete with the packed size.

IMO, these Klymit pads are in a class by themselves, because their design and features are so different than all the other pads. It makes comparisons and categorizations very difficult when the Klymit pads are included.

[Nick G]

Thanks Tom, that's actually a lot of thought about the Klymit pad which I hadn't gotten to yet. I'm looking for an inexpensive pad system which work with my 0 degree quilt, something that my Inertia pads simply cannot do, no matter how much I like them.

So here are my thoughts on other pad considerations:
First, I'll address the obvious factor of cost. All of the top five pads are out of my price range at the moment, except for the Ether Thermo 6. Unfortunately, I can't find anywhere which sells this pad currently–does anyone happen to know where I can get one?

By the time we move down the list to an affordable pad, we've already lost 40% of the weight efficiency, which is a shame. That's life, and it is a corresponding 90% decrease in price. A great deal, to be honest.

There are 3 pad options that are both affordable and fairly efficient: the GG nightlight, the Bivysack.com 1/2" Winter pad, and Lawson's new EVArest pads. I will surely want some full length insulation in winter, so the GG Nightlight won't be enough on it's own.

I'm planning on combining the Nightlight with either the Bivysack.com pad or the EVArest. Mostly, I'm waiting to see if Lawson comes out with a thicker pad any time soon. A nice thick version of the EVArest would be a huge help. Come on Lawson!

[Tom Lyons]

I didn't hear about the Lawson pad until after I had just purchased the GG Thinlight 3/16" evazote pad. But I'll upgrade when I wear out this GG Thinlight. The 3/16" Thinlight is pretty close to the 1/8" Lawson pad anyhow.

I do sympathize with quilt users in this situation. The performance levels drop off precipitously when the price goes under $100 with the current crop of inflatable pads.
The weight goes up, the R-values go down, and the bulk goes up.
If I were in that situation, I might be tempted by a POE(Hyalite) Peak Elite AC women's pad for $89(or cheaper if you can find one on discount). It's 66" length, and it has a higher r-value than the men's model, and doesn't cost any more than the men's model. You could combine that with a Lawson pad or two.

POE is now "Hyalite".
It appears that they did not carry the Ether models over when they changed names.

[David Olsen]

Durability is another factor in sleeping pad usage. I am not sure how one would
measure it. On CCF pads, tear strength could be a factor, inflatables, puncture resistance.

[Nick G]

Tom–thanks for the tip about Hyalite. I'm adding some of their pads now. The men's and womens AC pads list the same R Value of 2.5-4.4. Do you know why there are two drastically different warmths listed? I split the difference with 3.5, but I figure that's not the best way to do it. I don't see the difference you mentioned between men's and womens–the only thing I see according to their site is that the women's weighs an ounce more and is a bit smaller.

[Tom Lyons]

Well, in the old POE line-up, the women's was rated higher, so I thought it was still that way. With the women's being smaller and a little heavier, that leads me to believe that they still insulate the women's pad more than the men's. Perhaps they have their specs wrong?

Anyway, the 2.5-4.4 rating comes from a dual amount of insulation content. The 4.4 is under the torso, and the 2.5 is under the legs.

[Nick G]

Check out the spreadsheet!

Hyalite's closed cell foam pad just cornered the market completely in my book. Is this 4.0 R Value to be believed?

If it's even close, that makes this by far the most efficient and certainly the cheapest (for the R-value) pad on the market. I'm going to order one ASAP unless I hear otherwise. There must be some fundamental issues present or something, because it doesn't make sense otherwise.

[Tom Lyons]

I don't know about the accuracy of that r-value, one way or the other.
I just don't have any experience with it, nor have I heard anybody reporting about it.

But it sure does look like a good one, if indeed it is accurate.

Regarding your new table entry, you have the thickness column listed in inches, and you list the spec of the Hyalite Classic CC in centimeters(1.25) when actually it is .5" thick in inches. That entry should be corrected.

[Nick G]

I found some info on this site that says Hyalite/POE R Values are not to be trusted.

Wish there was a BPL test somewhere which would give more accurate numbers. Ah well. I added a note into the notes section, but otherwise we'll have to wait for more information.

[Jerry Adams]

"Wish there was a BPL test somewhere which would give more accurate numbers"

Roger is working on such a test:
http://www.backpackinglight.com/cgi-bin/backpackinglight/testing_thermal_insulation.html

That was more of a description of his test, and he's going to have another article with more data on more mats sometime in the future

[Raymond Estrella]

What there needs to be is one credible testing facility, like a mini ASTM International (the people that test the r-values of construction insulation among other things) that every manufacturer would use. They would get the pad and post the numbers, period.

Things like "perceived r-value" would go out the window as only hard data would show.

[Lawson Kline]

Thanks for including my pad in your spreadsheet.. I plan to add a 1/4", 1/2" and then probably a 3/4" or 1" convoluted pad.. Does anyone know if Thermarest has a patent on the Z fold part of their pads? I would imagine not since GG pads can also do this.. I have looked it up but I can't find anything so does anyone know something I don't? Thanks again, Lawson

[Nick G]

I know this is a strange world, but I honestly can't imagine being able to copyright the concept of a folding sleeping pad. It's not exactly a brilliant design breakthrough (and its used in quite a few pads). No actual information on that front though.

No problem on the pad spreadsheet. One of my main expansions to the data set was to add in a bunch of the BPL small businesses we love to support. The original list I believe was generated off an REI datasheet, which doesn't have any of that information.

Any idea when the new pads will be available?

Edit: I've downgraded the Hyalite pads based on customer reviews to a vague approximation of a likely R-Value. Honestly, by lying about R-Values we are left with no information, except that Hyalite is in the business of deceiving its customers.

[George Geist]

Hi Nick,

Did you and Kevin miss the article that Roger and Will did last Fall?
https://www.backpackinglight.com/cgi-bin/backpackinglight/airmat_sotmr_part2_2011.html

This article gives a big spreadsheet of actual measured "R" values
for a couple dozen sleeping pads. And also includes a data on
affect of thickness, different insulation methods used by the pads,
dimensions and more.

It is a must read for folks interested in r-values of sleeping pads.

Al

[Ross Bleakney]

Great stuff. One of the tricky things in all of this is how to measure R-values. Generally speaking, my guess is that they are measured by how much heat is lost to the ground (that is how the BPL test was done). This makes sense, of course, since most heat is lost to the ground. However, some heat is lost to the air. This is why foam is more effective when placed on top of a NeoAir, instead of underneath it. If all the loss was due to the ground, then it wouldn't matter. But since the NeoAir loses more to the surrounding air (even if it has the same R-value as the foam) it makes sense to put it on top (where there is a bigger potential for heat loss given the bigger difference in temperature between your body and the surrounding air). The NeoAir loses more to the surrounding air in part because it has a much bigger surface area. A foam mattress with the same R-value is much thinner. As a result, it loses very little to the outside air (on the edges).

Things get even trickier when it comes to losing heat on the top of the mattress. Depending on how the sleeping bag/quilt sits on top of the mattress, you may have very little, or quite a lot of heat lost on the upper surface. It's hard to measure for this as well, except to say that mattresses that are less prone to heat loss on the sides are probably less likely to lose heat on the top as well.

[Paul Hatfield]

> Hyalite's closed cell foam pad just cornered the market completely in my book.

I think you are forgetting how bulky a 1/2" thick pad is.
Just the foam itself is bulky, but since it must be rolled up, it's even more bulky because the foam will not roll very tightly.

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