Sleeping Pad R-Values: Not That Useful

The R value as reported does appear to be very low for foam pads – or should I rather say, the temperature rating of foam pads implied by R values appear low compared to inflatables.  Any experiences here?

I’ve camped out in the snowy mountains in the snow many times with a 10mm and finally an 11mm foam pad ($10 at a hardware store) – no issues, and did not feel the cold coming through.  Hard to say how cold it was, -5 to -10?  In the snow a foam pad is also very comfortable as you can mould the shape of the floor.

With more age I am now looking at inflatables for non-snow applications for more comfort, and also for stealth – having a foam pad makes it obvious what my intentions are and now living in Europe there is a grey area the legality of doing wild camping.

in Europe there is a grey area the legality of doing wild camping.
Not to the best of my knowledge, at least in France.
‘Camping’ is taken to mean caravans and big tents and BBQs, and has to be done in proper camping parks.
But pitching a little tent up in the mountains for a single night is called bivouacing, and it is quite legal. We have done that many times over the years.

Cheers

Good to know.  In Germany “biwakieren” is tolerated above the tree line “in an emergency”.  But otherwise illegal.

It is therefore important (to me) not to advertise to avoid questions and crowds in the mountains.

Roger, what is your take on the warmth of foam vs inflatables?

what is your take on the warmth of foam vs inflatables?
Well, that is a bit complicated. Air mats are much softer, so you get a better sleep, but they can compress down so there may be cold spots where the thickness is much reduced. But, of course, if you are fast asleep you may not notice.

The other problem with airmats is that you can get leaks, so you end up with nothing. I have had that once or twice over a lifetime of camping.

We (wife & I) each use an Exped Synmat UL7 over 1/8″ of CCF. The CCF is as much to protect the airmat when on rough ground as anything else. We have slept on that combination down to -7 C. But there was thick snowgrass under the tent.

Cheers

To expand on warmth of foam vs inflatables:

It depends. Some inflatables are literally little more than air mattresses, which are comfy but excel at sucking the heat right out of you.

That’s where standardized R-value testing comes in. In theory you can say foam pad X is warmer or cooler than inflatable pad Y. In practice, the test misses some confounding factors. As do almost all lab tests.

Decades ago I also spent many nights sleeping comfortably on snow using a 1/2-inch (12 mm) foam pad of unknown R-value. Melted my way deeper on a couple of nights. Snow can be an insulator at lower temperatures. But for several reasons, I wouldn’t even try that now.

Some people sleep fine on cold nights using thin foam pads by carefully choosing well-protected and naturally-insulated campsites. And using the right sleeping bag or quilt, and shelter.

So it’s pretty hard to generalize.

But if you aren’t skilled at choosing warm campsites, or don’t have a choice, take an R 5 or warmer sleeping pad. Many people stack foam and inflatables to get there.

— Rex

I appreciated the mention of seasons when selecting a properly insulated pad. A 40deg F night in the summer is not the same as a 40deg F night in the “winter” (I speak of winter on California’s central coast). The ground, in my experience, was much colder on the winter night than the summer night, hence why I got cold in the winter and not in the summer, even though I used the same sleep system.

Adding to what was said above…

I tried an Exped Ultra 5R inflatable last night in the backyard and felt a definite chill through the pad. The Colorado ground was frozen, and the overnight low was ~20ºF. Adding a Nemo Switchback on top helped, and the whole thing was darn comfy. But it still wasn’t as warm as the REI Kindercone + Switchback combo I’ve used elsewhere this winter under similar or colder conditions.

Something about the construction of these pads alters the R-value, for sure. Either the Exped’s 4.8 is over-rated, or the Kindercone’s 4.5 is under-rated, or both.

I wonder if you could make a hybrid of the inflatable, reflective mylar style pads, and the self-inflating open cell foam pads, increasing the R-value, softening the noise and lowering the height, all in one…

The R value on pads is measured statically. As a person moves around on the pad at night, the stratified air in the pad moves around and mixes warmed air near the sleeper with cold air near the ground. Only insulation can minimize the air movement. 3-4 inch thick pad tubes, even w insulation, allow more opportunity for air movement. I love my comfy Exped, but if the ground is frozen adding a Thinlight pad makes a sleepable difference. Exactly why I keep my old Xtherm around for low 20s temps and lower. Not as much cush for the tush, but being warm leads to good nights sleep!

Interesting discussion. I’m developing an UL cot partly because of the issue of non reliability of air mats.

Said UL cot is comprised of bamboo poles reinforced on the outside with S glass and high strength epoxy, and spray foam on the inside. The poles are connected to/fitted into high density, thick EVA foam blocks (Yoga exercise blocks that I cut up).  Then polypropylene webbing goes the length and width connected to the bamboo poles with a strap cinch on one end and a sewn loop on the other.  I plan to use CC-foam on top of the straps.  Maybe also a down under quilt underneath it if it is especially cold (I’ll only be about an inch off the ground). I’m hoping that since the foam will be on top of suspended straps/webbing, it might make it comfortable enough to sleep on.  It’s been awhile since I could sleep comfortably on CCF on the hard ground.

I’m not fully done with the project, but judging from the weight of the materials so far, I expect the cot to be around 2 lbs. I would still use an air mat for regular backpacking trips.  This UL cot is for specialized, severe cold type expedition type trip where I need something extremely reliable.

Hi Justin

I looked at this myself a long time ago. There were possibilities, but they all ran up against the extreme pressure under the cot legs on top of the groundsheet.
How are you dealing with this?

EDIT: I have a steel & canvas ex-army (I think) cot which has steel rods down the sides and 3 steel legs underneath, going from side to side. A heavy beast, but so very comfortable! But the legs touch the ground over very small areas.

Cheers

Hi Roger, there are no typical legs to speak of.  Instead, there are thick high density EVA foam blocks that I used a hole saw to drill out holes about the diameter of the bamboo poles.  The reinforced bamboo poles slot/fit inside the EVA foam blocks.  There are 8 EVA foam blocks. The corner ones are longer than the middle side ones as to fit the head and feet poles along with the side ones better (more volume area to hold the poles). There are 8 22″ poles that make up the rectangle frame (1 horizontal one at the head, 1 horizontal one at the foot, and then 3 vertical ones on each side).

My concern is that the EVA foam, though high density and thick, will eventually compress too much. If that happens (and I suspect it will over time), I might replace them with waterproofed balsa or basswood wood blocks instead.  There will be a weight increase, but it will handle the compressive forces much better.

I’m fairly close to finishing.  I just have to sew the loops on the polypropylene webbing (1″ wide webbing that is rated for 300 lbs continuous tensile strength and 900 lbs temporary/sudden. There will be 2 length wise straps and 6 width wise straps, but I will experiment with the latter and see if I get away with less width wise ones).  I’ll be uploading pics etc to the MYOG section when I am finished.

Hi Justin

You can get EVA foam in densities ranging from EVA30 (30kg/m3) to EVA400 (400 kg/m3). That is a huge range. My off-the-cuff GUESS is that you could start with EVA100 and go from there. The stuff is not $$.

What you really need is to find a mfr within range. I did, and the mgr was very helpful, and willing to sell small bits for MYOG.

OK, the foam will be bulky, but I would mainly worry about weight.

Photos: these are an absolute MUST! We drool in anticipation.

Cheers

Hi Roger, have you ever seen those foam blocks/bricks made and sold for yoga use? That is what I’m using for the foam blocks. I bought two of those (7 dollars US for each) and cut them up into smaller cubes/blocks. Very light, but somewhat bulky.

Yoga use? Sorry, not seen.
Web crawl . . .
EVA foam, and cork ones as well. The cork is very light and a bit more solid.

Cheers

The place I got it from didn’t have cork ones. If the EVA foam doesn’t work out, I will probably switch to balsa wood. It is around 40% less dense than cork, and has better abrasion and impact resistance/durability than cork (at least this form of cork i.e pressed particle stuff, which makes it more crumbly). In any case, either one would need to be waterproofed for such an application, unlike the EVA foam.

Photos!
Cheers

I would like to see Roger doing Yoga :)

Roger doing 1/2 yoga:

I had black hair back then.
That was in Spain on the GR11.

Jerry wrote, “I would like to see Roger doing Yoga :) ”

Budding Bro’mance or just morbid curiosity…?

I jest, I jest.

Chaff, all is Chaff.