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Most of the advice I see on sleeping pads is along the lines of "for cold weather, get a sleeping pad with an R-value of 5+." I've also read that R-value is additive—that is, if you stack two sleeping pads, you can add their R-values together.

I have a Big Agnes Insulated Air Core Ultra Sleeping Pad with an R-value of 4.5. It's an air mattress made up of 3.25" air-filled tubes. I also have a bunch of Ridgerest closed-cell foam sleeping pads with an R-value of 2.

My Big Agnes pad is super comfortable, and looking at the R-value I was excited to take it winter camping. It was probably around 0ºF. I put down the Big Agnes on top of a Ridgerest for a theoretical R-value of 6.5 … and I froze my butt off all night.

FWIW, I'm sleeping in a Western Mountaineering sleeping bag rated to -30ºF or so. And I don't think it was down to other factors. I've been camping for many years in much colder temperatures, and I know how to sleep warm.

I figured R-value must mean something different when it comes to an air mattress, so I went back to using two Ridgerest pads (R-value of 4), which has kept me reliably cozy down to -35ºF. Or a Ridgerest and a more traditional Therm-A-Rest–style sleeping pad (i.e., about 1" thick).

A year or so later I took my cousin camping. He has the Klymit Insulated Static V Luxe SL sleeping pad with an R-value of 6.5. It's also a tube-style air mattress. I tried to talk him out of it, but he was sure he knew better. It was around -25ºF that night, and he froze his butt off. He was sleeping in a 20ºF sleeping bag inside a 5ºF sleeping bag, which are probably warmer together than my bag.

But I was just browsing REI's website and noticed this in the description of the Big Agnes pad:

This pad has an R-value of 4.5, which makes it best for adventures in cold weather; it provides considerable insulation from ground temperature

Most sleeping pads we sell range from 1.0 (good for warm weather) to 5.5+ (for use in extreme cold); the higher the R-value, the more insulated the pad

And I just can't square that with my experience. It seems to me that something about sleeping pads with lots of air in them makes the R-value less reliable. My hypothesis is that at temperatures substantially below freezing the air in your mattress is going to be cold. And cold air next to your body means you're going to feel it. So the less air between you and the ground, the better.

Can anyone explain this better?

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  • Honestly, I thought about the question as asked again and I think it needs to be rephrased. Right now, there is no way to answer it objectively. You're pretty much asking us our opinion on how we trust manufacturers with their testing based on your own anecdotal experience, but it will only yield opinions, unless someone has access to a testing lab.
    – Gabriel
    Jul 6, 2021 at 16:08
  • I guess I was hoping someone would come in and say "I'm an experienced winter camper and actually air chamber mattresses keep me toasty warm" or "yes you're right, air chamber mattresses are poor in extreme cold for these reasons … "
    – samglover
    Jul 6, 2021 at 16:12
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    The problem is the question can be boiled down to "can we trust mattress R-rating". Nobody will have an objective, cited answer to that except their own experiences. But everyone's setup, body, and weather will have been different so I don't know how any meaningful conclusion can be extracted from that.
    – Gabriel
    Jul 6, 2021 at 16:16
  • Sort of. I assume R-value is an objective, lab-tested rating. But I suspect the test doesn't accurately reflect real-world conditions. It looks like the lab test sandwiches the material between two chambers and compares the temperature transfer. But in extreme cold use, the ambient temperature comes in "from the side" in a way it couldn't in the test. Maybe. I'm not sure that should matter. I need a scientist!
    – samglover
    Jul 6, 2021 at 16:20
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    For what it’s worth: My girlfriend’s Therm-A-Rest Women's Trail Lite with R=4.5 feels much warmer than my NeoAir® XLite with R=4.2. I froze my ass off in ~0°C weather but was perfectly fine with her Trail Lite. Even my old original Trail Lite with R=3.2 was warmer than the NeoAir.
    – Michael
    Jul 7, 2021 at 13:29

3 Answers 3

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I think your experience also depends on how you stack the pads. I’ve found that the foam pad needs to be on top, I suppose because otherwise your body needs to heat up all the air in the inflated pad?

I did an experiment when winter camping where I had a ridgerest-inflated pad stack sleep system and the first night I put the ridgerest on bottom (more comfortable) next to the snow. I froze my butt off. The second night, I put the ridgerest on top and the inflated pad on bottom - I was MUCH warmer! The first night I slept terribly, the second was great! I haven’t found any advice on the stack order, but I did talk with a physicist friend who confirmed that (theoretically) the foam pad should go on top to keep you warmer.

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My experience with inflatable pads is that they work just fine if you're not so heavy that you crush it down to effective non-existance under the pressure points. The outcome of this issue being that regardless of the theoretical value, their R value is 0 in practice.

Closed cell foam doesn't have this problem and remains pretty close to the theoretical R value.

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  • I can see how that would be the case, but I don't think it applies here. Neither my cousin nor I are heavy enough to crush an air mattress to non-existence. There is still plenty of space between my body and the ground when I use one.
    – samglover
    Jul 6, 2021 at 15:49
  • @samglover under your body yes, but what about under backside/hip and shoulder, those are the high pressure points
    – Separatrix
    Jul 6, 2021 at 15:51
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    I guess you're just going to have to trust me on this. Or I guess I could take pictures, but I promise I'm not compressing it anywhere near its full thickness, even at my pressures points. It's actually quite stiff when fully inflated, and that's how I prefer it.
    – samglover
    Jul 6, 2021 at 15:59
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    @samglover I'm happy to trust you, I just wanted to be sure you understood where I was going
    – Separatrix
    Jul 6, 2021 at 16:48
  • The thing is supposed to be 8cm thick, I doubt there would be pressure points deep enough to touch the ground. But the mattress appears to use "sewn-through" baffles, so there would be points without insulation between you and the ground
    – njzk2
    Jul 10, 2021 at 22:07
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You need to bear in mind that the classic Air Core is a straight baffle mattress. The structure doesn't prevent convection very well. It relies on the synthetic fill to do that job.

The Ultra model looks like it's a straight up air mattress with synthetic fill mattes on the top and bottom. It will still be bad for convection, but at least there's some conduction mitigation between the ground/air and Body/air.

When they test a new mattress, it is probably in ideal conditions, with fluffy new fill. Several factors can affect R-rating:

  • Depending on how you store your mattress, you could have damaged the fill so that it lost a lot of loft permanently.
  • If you inflate it by mouth, you could introduce moisture in the fill that when frozen makes it clump and collapse, severely reducing its performance.

I don't doubt the lab results, but different mattress designs will be less affected by age and potential handling or storage issues.

Anecdotally, when I worked in outdoors retail, I never recommended Big Agnes. They were the most uncomfortable, least insulating mattresses I had ever tried in the field.

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  • Hm. Interesting. I store it the way it was stored in the package: folded in thirds the long way and rolled, then put in a stuff sack. I inflated it once at home before taking it winter camping, so I don't think that's the issue. I don't think there's actually any fill in it, though. I think it's just air in the tubes, and the insulation is on the top and bottom surfaces. I suppose moisture introduced by my breath is possible, but that seems like a design flaw if so.
    – samglover
    Jul 6, 2021 at 15:53
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    @samglover Big problem right there. That kind of mattress should be stored like a sleeping bag to preserve its qualities (i.e. out of the package, uncompressed). By opposition, the TaR NeoAir designs can be stored rolled in their bags without much adverse effect.
    – Gabriel
    Jul 6, 2021 at 15:55
  • I think you're thinking of a different kind of sleeping pad. The Big Agnes is just tubes of air. There's no fill to compress.
    – samglover
    Jul 6, 2021 at 15:56
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    They could also be outright lying. AFAIK there’s no independent body verifying their claims.
    – JonathanReez
    Jul 6, 2021 at 15:59
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    Right. I just looked up that particular model. I guess Big Agnes changed the way they insulate it (compared to earlier Air Core models). But it's still a synthetic fill, just in a matte form. It can still be damaged through compression.
    – Gabriel
    Jul 6, 2021 at 16:00

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