Carol D commented on our post about down filled sleeping pads.
“I have owned a Downmat 9 for a couple of years and agree that they are WAY more comfortable than even the thickest Thermarest. However, camping in snow is problematic and the Downmat itself is NOT warm enough. My husband tried it the first time at about -5 celcius, in a tent on snow, with nothing else underneath the mat and was cold all night. He had on all of the available clothes, including a down jacket inside his winter weight sleeping bag and even that didn’t help. Last night I tried the mat outside at -12 Celcius, with a Ridgerest underneath and a winter weight down sleeping bag (rated to -25). I was relatively warm with a moderate amount of clothing on but I could feel the coolness from underneath. If it was much colder outside I think I would have had an uncomfortable night. I think the problem is that the air space in the Downmat is too thick for your body to keep warm when it’s getting cooled from the ground underneath. A Ridgerest underneath isn’t quite thick enough to offset the problem. Plus, the Downmat is quite wide (several cm’s wider than my mummy bag on each side) so much of it is exposed to cooling by the outside air. I still love the Downmat for comfort so I think next time I’ll try a thicker foamie underneath the Downmat, full length, and sleep inside a tent. Hopefully that will be warm enough!”
I suggest the combination of using an inflatable pad on the bottom and a closed cell pad on top for winter camping. It seems a bit counter-intuitive to use the inflatable on the bottom but it ends up acting like a balloon and floating the closed cell pad off of the cold snow. Inflatable pads provide superior comfort but you can get cold spots where hips or shoulders compress the pad. Closed cell pad provide superior insulation but don’t provide much cushion. This counter-intuitive stacking of the two is worth trying if you are going to be spending a lot of time sleeping in the snow.