Winter air mattress AND closed cell foam pad

[Eric Blumensaadt]

We all hear of people saying they supplement their insulated air mattresses with a closed cell pad like a Therm-a-Rest Ridgerest.

People use this combo with the closed cell pad on top of the air mattress as well as beneath  it.

I always put it beneath B/C I want to reduce convection within my insulated air mattress.

WHICH IS BEST?

[Edward John M]

What works for you personally is “best”

What is warmest might not be the most comfortable.

I’ll skimp on the sleeping bag to get more comfort and I have tried both methods; putting a thin CCF over the S2S comfort plus XL the initial warm feeling was appreciated but it was hard to keep in place but it only takes the air mattress a few minutes to warm up and I feel that both methods are equally warm over the course of the nite. On snow I use 3 mats if it’s really cold tho a very thin plus a RidgeRest then the Comfort plus. I just find that the CCF on top seems to be more sweaty feeling and that is uncomfortable for me

[David P]

I also use 3 mats in winter inside a MLD water resistant bivy

from ground up:

Emergency blanket ground cover, bivy, thermarest z-lite, 1/8” ccf, thermarest neo-air.

Works nicely for me. The ccf is pretty grippy and keeps sliding around to a minimum. The z-lite doubles as my snow mat for standing or sitting on while cooking, changing footwear etc. I cut it down into  two sections that I can reattach together with cam snaps, one 9 panel and one 5 panel. In summer, my son uses the 9 panel section as his mat.

[Matt Dirksen]

“I always put it beneath B/C I want to reduce convection within my insulated air mattress.”

How does putting the ccf pad underneath the air mattress reduce convection? If anything, I’d guess convection would increase in this arrangement.The impact force of body movement would be damped by a ccf pad on top of the air mattress, thus decreasing internal convection.

(p.s. here’s a good discussion from 2014: https://backpackinglight.com/forums/topic/94822/ )

[David Thomas]

What works best is whatever you’re least likely to slide off of in the middle of the night.  Differences in the R-value of the air gaps between pads or any radiant exchange effects will be very minor in comparison.

Thermarest once sold a slightly sticky goo in an aerosol can to spray onto your pad so it was less slippery.  And some pads come with a snail trail of something like contact cement. I suspect that would help one pad stick to another.

Or just 2 or 4 short lengths of tape to secure the pads together at the ends

[Eric Blumensaadt]

Matt,

I meant that convection due to cold from the bottom of the air mattress causes more convection when the air mattress is on a tent floor on snow. With a CFC pad beneath the air mattress there is less convection within the air mattress.

But David is likely correct regarding “best” is “… whatever you’re least likely to slide of of in the middle of the night.”

[Jerry Adams]

“Thermarest once sold a slightly sticky goo in an aerosol can to spray onto your pad”

I remember that.  It worked.

You could probably put silicone/mineral spirits or PU sealant like McNett Seam Grip

[Matt Dirksen]

“I meant that convection due to cold from the bottom of the air mattress causes more convection when the air mattress is on a tent floor on snow.”

I get it.

(So assuming there’s no body movement on the pad for a moment ) you are thinking that the ground being colder it might create more convection, right?

If so, keep in mind that for an increase in convection to occur, there would need to be a greater temperature difference between the top and bottom surfaces of the air mattress.

Therefore, if the ccf pad were on top, the top surface of the air-mattress would also be be cooler as well, thus reducing convective currents (since the ccf pad is inhibiting heat from getting to the air mattress in the first place.)

[Rex Sanders]

Related question: Some people put a smaller CCF pad under/over their full-length inflatable sleeping pad and claim the R-values still add up.

My brain sputters trying to figure out how the cold/heat doesn’t just go through the inflated parts that aren’t protected by the CCF pad.

But I’ve never tried it, maybe it does work.

Has anyone tried it? Does it work? Can you explain it?

— Rex

[Roger Caffin]

Good question.
The most squashed areas of your airmat are under your hips and shoulders. If the CCF pad can cover those areas, the rest won’t matter much. The rest of the airmat will be well-inflated by your weight on shoulders and hips.

Cheers

[Alex H]

The old standard advice was ccf on top I think to reduce the convective loss from the airpad but now I wonder with many of the new airoads relying on aluminized layers for reflected heat instead of actual insulation wouldn’t the ccf on top then reduce the amount of heat reflected back to the body?

[Todd T]

wouldn’t the ccf on top then reduce the amount of heat reflected back to the body?

That’s not how those radiant barriers work.  They limit the heat radiated across the air gap within the pad.

[James Marco]

Alex, very true. The thicker the film the greater the reflection, till it reaches maximum (when it absorbs more that it “reflects.”)

There are several mechanisms involved. Generally, a very thin plating of a molecule thick will work, however this is nearly impossible to produce. Paint films are several hundred thousands of molecules thick for comparison (depending on the pigment.) To continue the analogy, it leaves gaps in the surface. Even aluminum foil is somewhere in the neighborhood of 20,000 atoms thick. But they all have imperfect reflecting surfaces. Aluminum foil is around 95% reflective, but Mylar is only about 80% reflective to IR when new.

Some IR is picked up and re-transmitted as is most radiation in the lower end of the spectrum, often shifting down in frequency length while warming the material. (It can also up-shift such as glowing metal after getting the object very hot.)

Soo, to sum it all up, a SECOND piece of mylar film does help but only about 0.20×0.8 only to have most of the IR reflected off the first surface again and AWAY FROM YOU…not real helpful to a backpacker. This is ONLY a quick overview and by no means comprehensive. But two layers don’t really help except as the middle substrate will be warmed by absorption. Really, for backpacking, not worth the effort of carrying it. In every case, a single reflective layer is the only useful one. But, a space blanket makes a fair ground cloth.

If you can bond a sheet of AL foil, (at about 3oz) to a flat CCF pad over an inflatable pad, you can pretty much ignore the internal baffling of an inflatable pad. The lost IR (or “heat” if you will) can be used to warm the air slightly. IR radiation and molecular movement(actual heat) are different animals, though, we interpret them the same way through our skin.

The typical aluminized pad (say a Zrest) will help, but somewhat less than mylar…I would guess about 30-40% reflectivty. So, using two would help slightly (I would guess about 1%) but this is about the same as using a single piece of mylar and the mylar is lighter. This is for IR only, of course. All CCF will reflect and absorb some… Mylar was chosen as a good compromise between IR reflectivity and weight. None of this includes actual Rvalues, of course. Pads can vary in thickness and configuration.

[Roger Caffin]

To my mind, the temperature difference between you and the ground is not that high, so the radiant heat loss and the effect of reflecting layers is mainly in the mind of the marketing department.

Our practice is to always put the CCF layer below the airmat, for two reasons:
1) to protect the airmat from any spikes on the ground which might damage the airmat. This applies mainly when you are not on snow.
2) to isolate the airmat from the condensation which forms on the groundsheet. This applies strongly when you are camping on sub-zero snow. You can not prevent this condensation, although covering the groundsheet with gear along the sides of the mat will help.

Cheers

[Matt Dirksen]

“…is mainly in the mind of the marketing department.”

+1 to that.

Now Roger, don’t you typically use a Down Insulated Air Mattress?

Also, thanks for the note about floor condensation. A good reason to separate the air mattress from the floor of the tent. Personally, I sandwich my air mattress with a pair of 1/8″ ccf pads. If it gets colder, I’ll use more ccf.

Also, on our Scout winter campouts (where I’m not far from the car), I bring a handful of kiddie snap together foam pads, and use them UNDER the tent. That way they protect the tent, add a little R value, and keep the condensation off the floor entirely:

[Roger Caffin]

Hi Matt

Those snap-together mats look very neat.

Most of the time we (Sue & I) each use a full-length Exped Synmat UL7. It’s an airmat with very light insulation inside it, similar to what you find in synthetic bags but much lighter (brand unknown). We have used them down to -7 C, but not on snow.
Under them we normally have 1/8″ CCF mats.

On snow we use either two very old Therm-a-Rest Deluxe mats (self-inflating foam) or one full length Mammut Lightpump (airmat, internal pump, fluffy insulation) and one short Exped downmat (internal pump, down).
Under them we normally have 1/4″ CCF mats. These have the mold skin on one side, which goes downwards as that side does not absorb any water. They were cheap as they were actually factory off-cuts from a huge molded slab of foam – it’s how the stuff is made.

HTH
Cheers

[Eric Blumensaadt]

I think I am still of the “CCF mat under the air mattress” persuasion.

That catechism teaches that, “It is better to keep the air mattress from the cold than deal with high convection.”

 

[Jeffs Eleven]

I put my ccf on bottom and im warm. Plus i believe its easier to keep on top of your air pad on top of your ccf. I think keeping the ccf on the air pad AND under me is more frustrating.  It seems like the ccf sticks into the snow and doesnt move then it stays in place and all i have to do is keep my xtherm centered and thats relatively easy.   And anecdotally i dont get cold (finally!) so IMO ccf under

[Adam G]

I put it below the inflatable pad

1) I find it more comfortable. I use the Z-Lite Sol which is bumpy.
2) I use CCF pad for sitting around camp, so it does accumulate snow on it, and I’m not keen on sleeping on melty snow. I try my hardest not getting snow or water on my inflatable so it doesn’t seep into the bag.
3) It’s must easier to shove things between the inflatable and the CCF. I throw my gaiters in there so they don’t freeze and become impossible to put on in the morning.

[Jon S]

What works for me is to have my two pads inside my bivy sak to keep everything contained where one is less likely to become separated from everything.

The trip I did last week in temps of -35F (not including windchill) I used my Goretex Bivy, Thermarest Z-Lite pad (on bottom) and a Thermarest Neo-Air Xtherm pad on top. The sleeping bag I used was the Western Mountaineering Kodiak down bag rated at 0F. Was plenty warm but I made sure to stay hydrated (drank 110 oz of water/gatorade before going to sleep).Drank over 140oz water throughout the day as I was 11 miles out.

Hydration and nutrition are the key though.

 

[Roger Caffin]

@Jon

Not sure I understand. You say you were using a bag rated at 0 F in temps of -35 F, and you were plenty warm?
More details please!

Cheers

[Ryan Jordan]

Erik Normark (scandinavian youtuber) puts the CCF on top, which was interesting.

I tried it. I liked it – for comfort. It felt weird and different and good.

But I felt colder. But that was a long, hard day, and I was pretty trashed.

I’d like data. How should we prove it with data, which one is better?

[Edward John M]

I echo Rogers request for more information Jon, I was looking at that sleeping bag myself but the information given to me was that is was inadequate at -35f even with  down clothing on. Survival yes but not comfort. Note that I am a big feller and there would not have been room inside a long length bag for my big down parka

[Matt Dirksen]

“I’d like data. How should we prove it with data, which one is better?”

Obviously the term “better” needs to be narrowly defined, since there are many anecdotal and subjective reasons which compel a person to put a ccf on top OR below which have good merit, and work perfectly well for the user.

However, if you are specifically referring to the best arrangement to create a superior insulator, it’s true that “on paper” the arrangement shouldn’t matter whatsoever, since R values are simply additive.

But we are dealing with two different types of insulators (one of which is semi-dependent on radiant energy transmission to become effective.) It is also pretty clear that there’s a lot experience out there that points to one approach being “warmer” than the other.

Here’s a way to collect some data for those inclined (and with the right “tools”): How about warming up a 50lb bag of potatoes to a certain temperature and stuffing the sack into a sleeping bag, then letting it “rest” over top of a ccf/air mattress system for the night, while data recording the heat loss in a variety of locations inside and outside the bag. Then repeat the experiment the next night with the pads reversed. But I’d also recommend making sure the ambient temperature is real cold. Anyone have access to a walk-in freezer?

Regardless, I see three reasons (supported by my own anecdotal experiences), why I believe a ccf pad on top would “technically” create a better insulator overall:

1) CCF pads have a higher R value per inch of material than their air mattress counterparts. They are also a stable insulator. When it comes to maximizing the reduction of heat loss, placing the highest R per inch material closest to the heat source seems to be intuitive to me. In this arrangement, I suspect one would burn less energy staying warm earlier in the evening than they would by “warming up” an air mattress, even if it’s theoretically possible the same number of calories might be burned throughout the night (which I still don’t believe would happen, due to reasons 2 and 3).

2) Because the firmness of the ccf pad will more evenly distribute a person’s weight over top of an air mattress, this will reduce “point loads” on different parts of the pad (especially under the hips, buttocks, and shoulders.) This will suspend the person higher above the ground than with the ccf pad underneath. Roger spoke at length about this issue in his 2011 sleeping pad review, and it seemed clear that air mattresses showed a much wider “R value range” due to their ability to be easily compressed.

3) People move A LOT while sleeping through the night (1.6 times per hour, on average). While a person’s movement has zero effect on the R value of a ccf pad, moving around on an air mattress circulates the air inside of it “resetting “it, so to speak. When I first started using a NeoRest many years ago, I very quickly observed the phenomenon the first time I went from my side to my back. Therefore, assuming the CCF pad is nicely coupled to the air mattress, I believe a ccf pad on top dampens the intensity of of a person’s movement on an air mattress, reducing the undesired air circulation inside of it.

My 2¢

[Roger Caffin]

moving around on an air mattress circulates the air inside of it “resetting “it,
That is true for something like the BA air mattress I tested in 2011, where the mattress was little more than a pool toy. But that sort of air mattress is not something you would take into cold weather.

It is not really true for two other classes of air mats: self-inflating foam-cored mats (eg Thermarests) and mats with internal ‘fluffy’ filling such as down (DAMs) or synthetic fibres (eg Exped Synmat UL 7).

Matt’s comments do not cover several other reasons for putting the foam underneath. You might want to protect your airmat from potential spikes on the ground: the foam can do that. You might want to protect your airmat from condensation and even ice forming directly on the inside of the groundsheet: the foam can do that.

Cheers

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