If you are using beneath your sleeping bag an inflatable pad such as a Therm-a-rest mattress and a closed cell pad, which one goes against the ground for the warmest configuration?

Thanks.

I've heard people say that the closed cell foam on top is warmer. But I put it on the bottom, on the theory that an inflatable pad that keeps the air in it is warmer than one that springs a leak.

Most thermarest models already have foam inside, creating the dead air space needed for insulation. Putting the CCP underneath helps with puncture protection, as Smoke pointed out. Other air pads without the internal foam/insulation do better with the CCP on top in colder temps from my experience, punctures be damned.

I use a thermarest Xtherm and part of it warmth comes from a reflective coating that traps heat. I wonder if putting a closed cell foam pad on top would defeat this feature?

I put a foam pad under my Xtherm mostly to protect the Xtherm but I also think it is the warmest configuration. I've been cold a few nights but it was not caused by my pad and mattress.

I use this foam pad that weighs less than 3oz.
http://gossamergear.com/thinlight-backpacking-pads.html

I started backpacking fifty-eight years ago, and I used an air mattress made of rubberized Nylon. You would think that that heavy material would be durable. But it was prone to leaks and I eventually gave it up in favor of foam pads. So I don't trust air mattresses.

I wouldn't carry a foam pad at all if I were not worried about my air mattress springing a leak. So I use the foam pad under my Thermarest NeoAir.

KC

While an air mattress might not get punctured by rocks and sticks, the pressure of something sharp on a seam will weaken it. Later failures are possible.
A pad under the air mattress will protect it. A pad over the air mattress will keep you warmer. Take your pick.

Closed cell pad under, if both types must be taken. I think either is adequate from an insulation point of view. Durability prize goes to the foam, comfort to the inflatable.

Z lite with BA air core. Nice thing about the Z lite is folding it two sections wide to sit your tired ass on.