Sleeping Pad R-Values: Not That Useful

[Rex Sanders]

Companion forum thread to: Sleeping Pad R-Values: Not That Useful

R-values alone are not enough for many consumers choosing new sleeping pads, and much of the current guidance is inconsistent.

[Jeff McWilliams]

I think the last part of the article is the most important.

REI and retailers are suggesting an R value of 2-3 as acceptable for 3 season use despite the EN standard for sleeping bag ratings specifying an R=4.8 during testing.

HOW can they ignore the sleeping bag testing protocol when recommending R values for sleeping pads?

I feel like they’re all giving hikers bad advice for sleeping pad values.

[JCH]

The 3rd post is a little early for thread drift, so apologies in advance, but this is one of my soapbox issues…

The only advice one should trust is experience…your own or that of someone who obviously has it.  You must fundamentally understand yourself…how you sleep, how you perform in the backcountry and what gear has or hasn’t worked for you in the past…and then, apply that knowledge and experience to decisions about new gear.  People would like to look at a number and say “That is what I need” … but it just doesn’t work that way.

This site has been invaluable to me over the past 15 years as I transitioned from LW noob to UL.  Without the experience, advice, explanations and general guidance of many of those on BPL the journey would have been much longer, much harder and much more expensive.  Example: I have experience with item ‘A’.  Someone here says “I used item ‘A’ for 4 years, then moved to item ‘B’ and it performed like this…”, that kind of input is gold!

BPL has lost a great many of those “masters” who helped me so much in the past, but that just means those of us who are left need to step up :)

[Mike M]

I had a couple of the original Neoairs- great pad and obviously a huge game changer for many reasons; later when the Xtherm came out, I grabbed a couple of those for winter camping.

Putting them on the scale, the difference was only a couple of ounces.  Obviously the Xtherm is warmer and it seemed kind of silly to own two separate pads (actually four for my wife and I) for the benefit of a couple of ounces.  I sold the original Neoairs and use the Xtherms year round now.

Well that was until the Uberlight came along :)

[Chris R]

If the ground is warmer than the air, would there be a cost to using a pad with higher insulation value?

[Matt Dirksen]

“If the ground is warmer than the air, would there be a cost to using a pad with higher insulation value?”

It’s not as much about whether or not the ground is warmer than the air, it’s whether or not the ground (or air) is warmer than your body.

Even if the ground is warmer than the air, it’s probably still colder than your body. Therefore, it will act as a heat sink and continue stripping your warmth away until you both reach equilibrium. An insulator will inhibit this process. The higher the R value, the lower the thermal conductivity so the less heat is taken away from you over time.

[Matt Dirksen]

“R-values alone are not enough for many consumers choosing new sleeping pads, and much of the current guidance is inconsistent.”

And thanks for speaking up about this issue, Rex.

My sentiments exactly.

[Tony Cyphers]

I agree with Jeff, above… along w/ the concluding sentence, “R-values alone are not enough for many consumers choosing new sleeping pads, and much of the current guidance is inconsistent.” And, remember that the sleeping pad is just one part of a complex system.

It’s nice that retailers are helping to guide consumers, but I feel savvy backpackers are knowledgeable and have understood this. More education is always better. Thank you for this article!

[Matt Dirksen]

“…despite the EN standard for sleeping bag ratings specifying an R=4.8 during testing”

which brings up another very important point:

In the EN sleeping bag testing standard, how was the R value for the sleeping pads evaluated?

Was the R value taken from the pad manufacturer itself, or was it independently tested? Because it’s now clear that some of ThermaRest’s R values on many pads have changed due to the new ASTM standard, even though the pads haven’t changed.

So if any of the pads used in the EN sleeping bag testing are Thermarest, their R values are now different as well. Therefore is their “recommended” pad R value a different number now?

[Chris Malnowski]

The only advice one should trust is experience…your own or that of someone who obviously has it.  You must fundamentally understand yourself…how you sleep, how you perform in the backcountry and what gear has or hasn’t worked for you in the past…and then, apply that knowledge and experience to decisions about new gear.  People would like to look at a number and say “That is what I need” … but it just doesn’t work that way.

Agreed, but consistency in how things are quantified for objective criteria is extremely helpful in that process.  If I know that I currently sleep on a Therm-A-Rest R-3 pad, but am a little chilly, I can only go to another TAR pad with any level of comfort that the next pad will be better.  I assume (and we all know about assuming) that TAR tests all their pads the same way, so I can go to a TAR R-5 pad and feel like it would help.  I have no idea how that translates to nemo’s temp ratings, or how my TAR R-3 pad compares to temp ratings… or how someone else’s R-values compare to TAR’s.  Now, if all pads are tested to same standard, at least I know I can move to a nemo/REI/BA/Exped with an R-value higher than 3 and feel comfortable that it should perform better (for me) than my TAR R-3 pad.

Does that make sense?

Chris

 

[Jeff McWilliams]

Well said, Chris.

 

[Jerry Adams]

yeah – testing gives you relative performance – if one pad is a little cold for you you can select another pad that’s a little warmer

It also depends on the rest of your insulation.  If you have a warmer sleeping bag, you can have a less warm pad

[Jeffs Eleven]

In the EN test they dont use a pad. Its a wooden bench from what i understand. They did the math to figure out what the R value is of the wood bench is and it is near 5. This is what i learned from the Mtn Equipment sleeping bag team amd ‘Dr Down’ (cant remember his real name) but he is one of a very few people with a Dr in insulation.

The dummy is in a weird manikin position and the fan blows from the top (which obv isnt real-world) so they do extra testing with people in a freezer who turn over and sleep on their side so that Mtn Equipment ratings should be more accurate in real usage.

But they dont use an actual pad from some manufacturer.

[Greg Mihalik]

^^^

So, using R-4.8 to evaluate sleeping bags was circumstantial, not a “design criteria”.

The question evolves back to “What R-value pad do you need for a given ground temperature?”, while acknowledging that we all aren’t 30 year old males.

[Rex Sanders]

The Kansas State lab employed by many US companies for EN testing uses 1.5 inch sleeping pads – it’s posted on their web site:
https://www.k-state.edu/ier/testing/2017%20Sleeping%20Bag%20Insulation%20and%20Temp%20Ratings.html

Other researchers use pads for EN testing since it’s required by the standard, including Sweden’s Lund University:
https://doi.org/10.1080/10803548.2010.11076840

— Rex

[Greg Mihalik]

^^^

From the PDF referenced in   https://doi.org/10.1080/10803548.2010.11076840

Multiply  m^2 K/W by 5.678 to get R-value.

Using 0.85 as a midpoint between 0.79 and 0.91 we get an R-value of 4.8, as mentioned by Jeff above.

Any insights on where the “standard” range originates? Why does EN 13357 choose this range?

 

 

 

[Greg Mihalik]

From this 2007  post –

“EN13537 assumes you are using a Thermarest Standard pad.”

Does anyone know which pad this refers to?

[Rex Sanders]

Unfortunately, the EN/ISO sleeping bag standards (part 1, part 2) are also behind an expensive paywall (1 CHF ~= 1 USD). And if it’s like most standards, it doesn’t explain the “why” of various choices; most of that is hashed out in committee meetings behind closed doors and in private email lists.

Standards are always imperfect compared to the real world; but for sleeping bags and pads, standards can help consumers choose between products, and we can add fudge factors based on personal experience.

If we have any. That’s where R-values really fall down. Most people understand temperatures; equating an R 3 pad to how warm I’ll sleep on a 30° F night without R-value experience is not obvious, and the available guidance is terrible.

— Rex

[Rex Sanders]

I’m 99% certain that the EN/ISO standard does not call for a specific make and model of pad. More likely the spec is like that quote in the Lund University paper, a “representative” mat that falls in a narrow-ish range of thermal resistance values.

Note that using a pad (on a board) is more representative of real-world use than the equivalent R-value of just boards; pads compress under body weight, boards, not so much.

Somewhere I read that Kansas State sleeping bag tests used the same Therm-a-Rest pad for years, until it wore out and they switched to a newer model TaR pad. In Sweden, they’re using something else.

— Rex

[Franco Darioli]

 

 

https://www.sis.se/api/document/preview/920965/

[Rex Sanders]

Thanks Franco!

For those of you possibly alarmed by the top of Franco’s snippet, the standard defines two testing positions for the manikin: (1) fully zipped up inside the sleeping bag and (2) head and arms out. The commonly cited EN numbers for sleeping bags use position 1.

— Rex

[Matt Dirksen]

I guess it’s time to repost this 10 year old document about the ASTM and the EN bag testing methods, and their respective issues:

https://www.outdoorindustry.org/pdf/EN13537Mccullough062209.pdf

 

 

[Rex Sanders]

Some of McCullough’s concerns in 2009 have been addressed in updates; the latest ISO standard is from 2016. That 2009 paper does provide more insight into the testing process and problems.

Lab testing can be much messier than people realize

— Rex

[Greg Mihalik]

nm

 

[Rex Sanders]

Here’s another scenario where R-values and poorly defined seasons won’t help, especially if you don’t hang out on BPL or r/Ultralight.

You bought a 30° F EN-rated sleeping bag plus an R 2.3 “three-season” Uberlite based on Therm-a-Rest’s chart. But you keep freezing your tush off sleeping mostly naked on 35° F nights. What do most people blame? The sleeping bag.

What’s really wrong? Sleeping pad probably, but could be many other factors, including poor site selection and not wearing a layer of light clothing and socks to match the EN testing specifications.

You don’t even think to try a warmer pad. And even if you did – how much warmer? An R 4.2 XLite seems like overkill since 35° F hardly qualifies as “winter” in many areas. And yet even the XLite might not be quite warm enough to support the EN rating of the sleeping bag.

R-values are valuable, maybe even necessary, but not enough. Especially when the guidance is confusing, inconsistent (even within makers and retailers!), and possibly wrong.

Add the other variables that go into sleeping warm enough, and you get frustrated if not hypothermic customers.

Like Tim Marshall from Enlightened Equipment, who at least gives R-value guidelines by temperature:

— Rex

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