This is the guts of the NeoAir.
As far as I know, the membranes are fabric, and the inner membranes are heat-reflective. Yes, you can get condensation inside, but absent any fill this may not matter. perhaps you will be able to drain it out easily.
The picture is from the official Cascade Designs press release. I hope they won't mind my using it here. (Somehow, I doubt it!)