I've seen this discussed elsewhere (without much agreement :smile:)
Thermally, it doesn't make any difference if the ccf mat is on top or bottom. The rate of energy loss (Er) depends on the temperature difference (deltaT) between you and the ground and the effective heat transfer rate of the system (Rs).
Er = deltaT / Rs
The R value is for the whole system - you can't add the individual r-values (unless both materials are solid and in good contact - which they are not in this case).
In practice, there *is* a small initial difference in rate of heat loss - until the layers reach thermal equlibrium (which will happen in minutes). However, the ccf mat on the bottom is a lot more comfortable !
This post has been edited by the author on 1 June 2018 at 20:35.
Suspect there's more to it than that @bernieq.
1) point compression: closed cell foam drops from its nominal R to much lower numbers where it is compressed. Eg hips, side sleeping. So I'd suspect it performs better for R where weight is more evenly distributed - ie if its on the bottom with the inflatable spreading the weight.
2) 'wrap'. Presumably there's an insulation benefit from sinking into your mat rather than lying flat on top. Draughts and lateral radiation from the underside of your body would be reduced by sinking into the foam. So foam on top?
3) Conductivity at skin / mat barrier. Inflatables are well insulated vertically but not horizontally. The external layer feels as if it conducts heat quite well. So that layer in contact with your skin may well be conducting heat away laterally to reradiate back into the ether. Foam will insulate as well laterally as vertically so should be better in this regard. Which I'm guessing is why foam feels warmer to the touch, even if the overall heat loss is higher. So foam on top?
Which all leaves me no clearer ad to which order is best!
This post has been edited by the author on 2 June 2018 at 08:22.
Yes, the very fine detail is tricky indeed. I suspect it doesn't make an appreciable difference. I will note that I was commenting only on heat loss through conductivity, not radiation or convection.
1. Fair point but I think the amount is insignificant. Many years on only a ccf mat without noticing cold points at hip or shoulder.
2. What you might gain from wrap (radiation) needs to be offset by what you lose from compression (conductivity).
3. Skin / mat barrier? You're tougher than me! I use a down sleeping bag between me and the mat :smile:
> Many years on only a ccf mat without noticing cold points at hip or shoulder
Interesting. Cold at compression points is _the_ reason I'd never go back to ccf. Guess it depends on sleeping position.