Winter hike: using 2 sleeping pads together, good idea?

Yes, it is perfectly acceptable to combine pads! A very common combination that people use in the winter is a regular closed cell foam mat (like a thermarest ridgerest) underneath a inflatable air mat. You get a boost in r-value, protection for your inflatable, and a backup plan incase your inflatable craps out. I see no reason why you can't use two inflatables instead of one inflatable and one ccf

I'm sure someone with more Science will be along, but in my experience a CCF pad beneath the inflatable works best. As I figure it, your body heat warms the air inside the inflatable. But the air in a second inflatable is only warmed by heat lost from the first, so you're putting your warm-air pad on top of a cold-air pocket. In other words, the heat you aren't losing to the ground is still being lost by the top pad, into the lower, leaving you on a colder pad. A CCF pad will block heat loss from the top pad better, and it's lighter. I find a RidgeRest SOLite under an insulated inflatable the warmest setup. Even just a mylar sheet under an inflatable seemed to help quite a bit when I was caught unprepared in the shoulder season. If a reflective coating is the 'insulation' in your second pad, just use something reflective and skip the cold-air-holder, I figure.

I agree with Konrad, I don't see why you couldn't. The only thing I would be concerned about though would be keeping the air pads stacked on top of each other throughout the night…

In winter I layer a ccf pad on TOP of my NeoAir. I have had quite the opposite experience as Bogs did when layering a ccf with an air pad.

After consistently using a 1/8" Thinlight ccf pad on top of my (original) NeoAir and having no problems, I decided one night to try the ccf pad under the Neo. I was immediately cold when I laid down and stayed that way. I laid still for an hour hoping that the Neo would soon warm up from my body heat, but it never did. After an hour I got up and switched the ccf pad back on top of the NeoAir. When I laid back down I felt immediately warmer, and it stayed this way throughout the night. After this experiment, I layer my ccf pad on top of my air pads when I need more warmth… If I only want to protect my air pad then I will put my ccf pad underneath.

OK, thank you for your comments.

I have a follow-up question: My winter hike is in France (Les Vosges) and expected temperature at night will be around 20-25°Fahrenheit (-5° Celsius), so for the moment it's not really that cold at night. Would the Thermarest Trail Lite (3.4 R-value) be sucifficient for that temperatures?

Everyone is different, but I personally would be able to keep warm with an r-value of 3.4 in those temps. I've used r-value of 3 in mid 20's F in a quilt with no problems. So yes, you should be okay.

Ok, thank you so much for your answer. As this is my first winter hike I can't fall back on past experiences so all your help is very much appreciated!!

Having spent many nights sleeping on the slow in Alaska in the winter, I had the same experience as Chad above.  Putting the CCF on top of the air mattress was warmer.  I think this is because the air mattress gets some side heat transfer due to convection that the pad reduces because by the time the heat is on the down side of the CCF, the temperature is less so there is less driving force for the heat to the air.  Maybe that is too technical of an answer but it seemed to work well even down to -40F.  The warmth from a foam pad is a beautiful thing.

My experience says that if the air mat is insulated it makes very little difference in the AM but it matters if the airmat has no insulation, in practical terms tho protecting the more fragile airmat takes precedence

So perhaps the best solution is for two thin CCF mats, one under and one over plus some cord or tape to hold them together

Almost 5 year old thread! Good bump.