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You are here: Home / Blog / Sleeping Pad R-Values: Not That Useful

Sleeping Pad R-Values: Not That Useful

by Rex Sanders on November 26, 2019 Blog, New Features

Overview

Lightweight backpackers have long complained about how hard it is to compare the warmth of different sleeping pads. Recently, three pad makers and retailers announced that they would use a new standard for measuring sleeping pad insulation. And in 2020, REI and MEC will require all their suppliers to report those values. At first glance, this looks great. But the devil is in the details.

For many years, pad makers like Nemo and Big Agnes have advertised temperature ranges without describing how they came up with those numbers. Others promoted R-values using different protocols. This made it almost impossible to reliably compare sleeping pads between manufacturers.

Then late last year, MEC, REI, and Therm-a-Rest announced that they would use a new sleeping pad R-value standard to measure their own products. And starting in 2020, REI and MEC will only sell pads furnished with standard R-values. Many people were glad that they could soon compare sleeping pads across manufacturers, like the EN/ISO 13537 temperature ratings for sleeping bags. But knowing the R-values of sleeping pads raises new questions.

What’s an R-value and how is it measured?

An R-value measures resistance to heat transfer through an insulating layer. An R 3 sleeping pad provides three times more insulation than an R 1 pad. But as one part of a sleeping system, you won’t sleep three times warmer.

R-values started as a way to measure building insulation. In this post, I’m using United States R-values; the rest of the world uses metric units sometimes called RSI. To convert from the metric values found in many scientific papers to US R-values, multiply by 5.68.

US R-Value Metric RSI (K·m2/W)
1 0.18
2 0.35
3 0.53
4 0.70
5 0.88

While the new R-value standard is behind a paywall, Outside described the basic testing setup: two plates at constant temperatures of 95 F (35 C) and 41 F (5 C) squeeze a pad to simulate human weight. Many other factors are under control, including pad inflation, ambient temperature, wind, and humidity. At the time of their announcement, only MEC, REI, and Therm-a-Rest owned the $50,000 machines required to measure sleeping pads using the new standard.

Sleeping pad tests in a well-controlled lab only go so far. Roger Caffin covers many of the pitfalls of pad testing for BPL in Apparatus for Testing Thermal Insulation Properties. Roger and Will Rietveld also go into more detail on the real-world performance of sleeping pads in Lightweight Inflatable Sleeping Airmats – State of the Market 2011 Part 1 and Part 2.

Many BPL readers understand R-values to some extent, but most consumers don’t. And they certainly won’t know what R-value of sleeping pad they need.

What R-value should I look for in a new sleeping pad?

If you know the R-value of your existing sleeping pad, soon you can decide if your next pad should be warmer, cooler, or about the same across many brands. But you’ll need more information if you don’t know the R-value of your current pad or you’re new to shopping for sleeping pads.

Unfortunately, the guidance from pad makers, retailers, and gear reviewers is inconsistent and prone to misinterpretation. For example, see:

1. The Therm-a-Rest blog What Is R-Value?

Sanders R Value 1

Therm-a-Rest chart comparing R-values to seasons. Credit: Therm-a-Rest.

2. Therm-a-Rest Ultralight Adventure pad finder:

  • R 2 to 3.3 – Three Season
  • R 3.4 and higher – Winter
  • R 5.7 and higher – Extreme Cold

3. REI Expert Advice How to Choose Sleeping Pads

“Thicker pads generally offer higher R-values and the average summer camping pad should be around 3 or higher. Campers who sleep cold, often women, may want to choose a pad with an R-value of at least 4.”

4. REI in-store sign next to sleeping pads:

Sanders R Value 2

This sign in the REI Marina, California store compares R-values to seasons, with more detailed explanations of seasonal conditions. Photo credit: Rex Sanders.

 

5. Philip Werner’s Section Hiker blog Sleeping Pad R Values

  • “For winter backpacking and camping, an R-value of 5, or higher, is recommended.
  • For three-season backpacking and camping, an R-value of 2, or higher, is recommended.
  • An additional R value of 1 is usually a good hedge for women and other cold sleepers.”

6. Outdoor Gear Lab How to Choose a Backpacking Sleeping Pad

“We have found that pads with R-values between 2.0 and 3.0 generally work well for three-season use but should be supplemented with a foam pad for use in the winter where an R-value of around 5 or above is ideal. Pads with R-values lower than 2.0 are great for summer, but you may want to supplement them with a closed cell foam pad on colder nights in the spring and fall.”

All this advice shares two serious shortcomings:

  • Seasons in coastal Hawaii are very different from northern Minnesota, so “winter” low temperatures could be anywhere from +40 F (4 C) to -40 F (-40 C).
  • Poorly-defined seasons don’t match up with sleeping bag EN ratings by temperature, which is where most people start their shopping.

But in one important way, all this guidance is wrong.

How do sleeping bag temperature ratings relate to R-values?

Most people want their entire sleep system – clothing, sleeping bag, sleeping pad, and shelter – to keep them reasonably warm at night. And many consumers focus on sleeping bag temperature ratings. For example, a warm sleeper might decide that for a trip with forecast low temperatures in the 40-50 F (4-10 C) range, a sleeping bag with an EN/ISO lower limit rating of 40 F (4 C) should work well. The EN/ISO testing protocol requires a zipped up sleeping bag with the hood cinched along with several other requirements including using an R 4.8 sleeping pad.

If your sleeping pad is substantially less than R 4.8, you’ll lose more heat to the ground, and you might not be warm enough in an EN 40 F (4 C) sleeping bag on a 45 F (7 C) night. I wrote “might not” because how warm you sleep on any given night depends on many other variables. One paper claims (PDF) that using an R 1.3 or lower pad could cut 10 F (6 C) from the effective rating of a sleeping bag.

Relying on EN/ISO sleeping bag temperature ratings argues for always using an approximately R 5 pad. This is more-or-less the approach taken by Zenbivy, who states: “only mattresses with R value 5 or greater will deliver full temperature rating performance from EN rated sleeping bags.”

Conclusion

R-values alone are not enough for many consumers choosing new sleeping pads, and much of the current guidance is inconsistent. Manufacturers and retailers who suggest lower R value pads for a wide range of temperatures could be seriously misleading buyers.

rei magma trail quilt review 2

You can’t look at a sleeping pad’s R-value in a bubble. Consider your pad part of an integrated system that includes the clothing you wear to bed, your sleeping bag or quilt, the type of shelter you’re in, the nature of the ground surface (snow, moisture, etc.), ambient temperatures, and of course, your own physiology. Photo: Ryan Jordan

big agnes, Nemo, rei, sleeping pads, sleeping systems, Therm-a-Rest, thermarest

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Home › Forums › Sleeping Pad R-Values: Not That Useful

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  • Nov 26, 2019 at 12:29 am #3620437
    Rex Sanders
    BPL Member

    @rex

    Locale: Central California Coast

    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.

    Nov 26, 2019 at 12:52 pm #3620483
    Jeff McWilliams
    BPL Member

    @jjmcwill

    Locale: Midwest

    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.

    Nov 26, 2019 at 1:21 pm #3620487
    JCH
    BPL Member

    @pastyj-2-2

    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 :)

    Nov 26, 2019 at 2:18 pm #3620491
    Mike M
    BPL Member

    @mtwarden

    Locale: Montana

    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 :)

    Nov 26, 2019 at 3:53 pm #3620499
    Chris R
    BPL Member

    @bothwell-voyageur

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

    Nov 26, 2019 at 4:28 pm #3620503
    Matt Dirksen
    BPL Member

    @namelessway

    Locale: Mid Atlantic

    “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.

    Nov 26, 2019 at 4:29 pm #3620504
    Matt Dirksen
    BPL Member

    @namelessway

    Locale: Mid Atlantic

    “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.

    Nov 26, 2019 at 6:54 pm #3620514
    Tony Cyphers
    BPL Member

    @pacrat

    Locale: PNW

    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!

    Nov 26, 2019 at 9:15 pm #3620551
    Matt Dirksen
    BPL Member

    @namelessway

    Locale: Mid Atlantic

    “…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?

    Nov 27, 2019 at 1:42 pm #3620599
    Chris Malnowski
    BPL Member

    @cmalinowski

    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

     

    Nov 27, 2019 at 1:48 pm #3620601
    Jeff McWilliams
    BPL Member

    @jjmcwill

    Locale: Midwest

    Well said, Chris.

     

    Nov 27, 2019 at 2:37 pm #3620604
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    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

    Nov 27, 2019 at 2:51 pm #3620606
    Jeffs Eleven
    BPL Member

    @woodenwizard

    Locale: NePo

    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.

    Nov 27, 2019 at 4:41 pm #3620616
    Greg Mihalik
    BPL Member

    @greg23

    Locale: Colorado

    ^^^

    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.

    Nov 27, 2019 at 6:29 pm #3620630
    Rex Sanders
    BPL Member

    @rex

    Locale: Central California Coast

    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

    Nov 27, 2019 at 6:58 pm #3620633
    Greg Mihalik
    BPL Member

    @greg23

    Locale: Colorado

    ^^^

    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?

     

     

     

    Nov 27, 2019 at 8:48 pm #3620677
    Greg Mihalik
    BPL Member

    @greg23

    Locale: Colorado

    From this 2007  post –

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

    Does anyone know which pad this refers to?

    Nov 27, 2019 at 9:01 pm #3620679
    Rex Sanders
    BPL Member

    @rex

    Locale: Central California Coast

    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

    Nov 27, 2019 at 9:07 pm #3620680
    Rex Sanders
    BPL Member

    @rex

    Locale: Central California Coast

    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

    Nov 27, 2019 at 9:55 pm #3620686
    Franco Darioli
    Spectator

    @franco

    Locale: Gauche, CU.

     

     

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

    Nov 27, 2019 at 11:34 pm #3620699
    Rex Sanders
    BPL Member

    @rex

    Locale: Central California Coast

    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

    Nov 28, 2019 at 2:17 am #3620718
    Matt Dirksen
    BPL Member

    @namelessway

    Locale: Mid Atlantic

    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

     

     

    Nov 28, 2019 at 3:17 am #3620735
    Rex Sanders
    BPL Member

    @rex

    Locale: Central California Coast

    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

    Nov 28, 2019 at 3:23 am #3620739
    Greg Mihalik
    BPL Member

    @greg23

    Locale: Colorado

    nm

     

    Nov 30, 2019 at 11:00 pm #3620985
    Rex Sanders
    BPL Member

    @rex

    Locale: Central California Coast

    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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