Backpacking and camping sleeping pads are rated using R-values which measure their ability to keep you warm when you lie down on the cold ground. The higher the R-value, the greater the insulating power. It’s much more technical than that, but that’s the gist of it.
But people really struggle with the concept of an R-value and its implications when it comes to backpacking and camping gear selection. What they want to know is a pad’s temperature rating, like the way that sleeping bags are rated. What is the coldest temperature I can still use this sleeping pad and remain comfortable? That’s the real question they want to be answered.
Here’s a table that shows how R-values correspond to Temperature Ratings. These are air temperatures, which people have easy access too from weather reports and historical temperature data published by companies like the Weather Underground that you can look up easily.
|Air Temperature (F):||50||30||25||10||0||-15||-25||-40|
|Air Temperature (C):||10||-1||-4||-12||-18||-26||-32||-40|
- R-values are additive, so you can combine two pads to increase your warmth level. For example, it’s common to carry a foam sleeping pad (usually R=2) in winter to use as a sit pad when eating and melting snow that you can place under an inflatable pad to increase their combined R-value for sleeping.
- Women need higher R-values pads because they have lower body mass than men. An additional R-value of 1 is usually a good hedge for women and other cold sleepers.
- If a pad model has multiple sizes, they all have the same R-value unless specified otherwise
- EN sleeping bag temperature ratings are predicated on using a sleeping pad with an R-value of 5 or higher. If you find yourself sleeping cold in temperatures where you’d expect your sleeping bag should keep you warm, it may be because your sleeping pad has an R-value less than 5.
It’s important to qualify the R-values in the table above. They are based on the R-value standard called ASTM F3340-18 which was spearheaded by REI, Exped, Thermarest, Sea-to-Summit, NEMO, Big Agnes, and Klymit that specifies a common R-value test methodology. It was necessary to define so that the R-values published by different companies can be used as a common method of comparison by consumers. Before that standard was formalized, every company had a different way of computing R-values, making comparisons impossible. You also had no real way of knowing if the pads had ever been tested, if the published R-values were estimated, or just made up.
Unstandardized R-Value Ratings
Unfortunately, many companies still publish sleeping pad R-values that aren’t measured using the ASTM F3340-18 R-value standard. Who are they? They include most of the offshore, fly-by-night brands listed on Amazon.com, Walmart, and Aliexpress like Sleepingo, Powerlix, Gear Doctors, ZOOBELIEVES, and others, as well as more established lower-cost brands like Paria Outdoor Products and Featherstone Outdoor Products. That doesn’t necessarily mean you’ll freeze to death if you use a pad rated with a non-standard R-value, but it makes them difficult to compare with pads from other manufacturers since they don’t use a common testing methodology.
If you do decide to buy a lower-cost pad from one of these manufacturers, I’d stick to ones intended for warm weather camping above 50 degrees F. Look at their online product reviews and if other customers endorse them in comparable conditions, they’re probably a reasonably safe purchase. For colder temperatures, especially those below freezing, I’d recommend getting a pad whose R-value has been rated using the ASTM F3340-18 R-value standard so you know exactly what you’re getting.
Feels contra intuitive to relate a condition to something that is above you, the air, to something that is beneath you, the pad en the ground.
How do the condition and temperature of the underground impact the minimum R-Value? Like dry, wet, frozen, rock or snow?
Air temperature is actually a pretty good correlate to the temperature of the ground’s surface which is the part you put your pad on top of. The state of the surface – dirt, water, ice, and snow is all a function of air temperature. The ground also provides some thermal resistence which is factored into the equation. For instance, snow has an R-value of 1. Anyway, this is why people have a hard time parsing R-values. But with the R-value measurement standardized, there is a common basis to make temperature correlations so humans can unerstand why they need.
If you try camping on frozen ground at 0°F (-18°C) with a pad of R-2 or 3, you’ll feel the cold coming up from below. It won’t matter how warm a sleeping bag you use, you’ll be cold. Your body needs to be surrounded by adequate insulation.
I’m known by family and friends as the fanatic (or worse!) who sleeps in the back yard on the coldest nights of the year. This chart corresponds quite well to my personal comfort needs as far as the pad under me is concerned. R-3 gets me to 25°F (-4°), R-5 gets me to 0°F (-18°C).
Any thoughts about putting the foam pad on top of the inflatable sleeping pad? I saw a video recently where the instructor who leads military SERE (Search/Evasion/Rescue/Escape) training recommended doing it that way to provide more separation from the ground.
I’m puzzled why the correlation between R-value and air temperature isn’t more linear. That puzzlement is not surprising, since I’m not a physicist nor a meteorologist, but nevertheless I hope you can shed some light on why the numbers don’t make a smoother curve:
50 to 30: 20-degree difference, 1 R-value difference
30 to 25: 5-degree difference, 1 R-value difference
25 to 10: 15-degree difference, 1 R-value difference
10 to 0: 10-degree difference, 1 R-value difference
0 to -15: 15-degree difference, 1 R-value difference
I wrote that off to human anatomy. I noticed it too.
I was wondering if there is a formula for determining R value based on the thickness of closed cell foam,and should the ccf pad be on the top or bottom of the air pad. Thanks!
Depends on the foam. I doubt it’s uniformly made. As for the stacking of the pads, I personally worry more about falling off a foam pad stacked on top of my 4″ air mattress than the other way around. But I’d hesitate to take a stand as to which is warmer and whether the difference has much impact since the circumstances in which it’s done probably vary widely in terms of external temperature, air movement, the impact of different physiques, and the body heat they generate. It’s certainly a question that keeps coming up.
I don’t know whether the position of the foam pad affects the total R-value of the combination, but I always put my foam pad under the air mattress to maximize protection against puncture and abrasion.
I bought a $30 R8 sleeping pad off of Amazon. it’s worked to temperatures as cold as -12 Fahrenheit in a -20° sleeping bag. I didn’t eat extra blankets I’m a small guy I don’t put off as much heat is a big guy yet I slept comfortably all night didn’t feel the ground underneath me. I’ve paid $150 for a 5.5 sleeping pad from one of the big names. and that was 10° f weather the same sleeping bag and I could feel the cold on my back. so what I tell everybody right now is by what you can afford if you spend $30 and it gets you through two trips you saved money.
articles like this is just written to push people just spend more money and these expensive name brands. those ultralight sleeping pads I’d rather have an extra pound on my back and stay warm for 30 bucks then save weight and still be cold for 150-200 bucks.
just remember people your ancestors probably slept on a wool blanket at some point and freezing cold temperatures.
Yes the r value matters but where you buy it doesn’t in these convoluted tests they keep throwing are anecdotal at best. but I can also tell you this every body is different and in cold weather, what works best for you may not work best for somebody else. there’s a lot of good information on this article but there’s also a lot of propaganda on this article as well. always test your gear because my -20 bag is warmer for me than my buddies -20 bag. My $30 sleeping pad works better for me then my buddies $200 sleeping pad. if you have friends test out their gear see what you like see what works for you ask around talk to people
Let me guess…you’re American. I love how you people deny science. It’s hilarious!
I’m not going to defend the guy because what he says is mostly pretty ridiculous. Equally ridiculous is your assertion that science deniers are unique to ‘merica.
He does cover a lot of ground.
Been giving this some thought. In my WFA course it was a common thread that one of the first things to address is getting the patient off the ground (the ground sucks the heat from the body). I feel it’s pretty clear that the R value rating is a good number to compare one pad to another – this one should be warmer/colder than that one. I do think in practice though the conditions you use that pad under though are going to partially impact how warm or cold it sleeps based on the air temp.
If I set up my sleep system directly on ledge/rock it’s going to sleep colder than if I have a few inches of forest duff under me which adds an insulation level. Or if I’m on a tent platform/shelter I don’t have direct contact with the earth but have air circulating underneath.
Lots of variables. Not suggesting the table above is wrong in any way but those variables, and others, can explain why an R3 pad and 20 degree bag might have been perfectly fine for a 5 degree night.
How much is the thermal resistance of a material affected by air temperature on its “other” side. Take building insulation. Does its thermal resistance change when it’s colder outside or does it stay the same? I sometimes wonder if people mistakenly view a sleeping pad as a source of warmth, rather than resistance to loss of warmth and whether the distinction matters.
Thermal rezistence (R- value) of pad is not affected it stays the same, but I’m sure the amount of heat which gets through insulation depends on what is on the other side, especially what thermal gradient (temperature difference) will be practically maintained.