In reply to andrew breckill:
down mat.
i was lucky enough to try an xtherm before industry release and indeed they are good, very good. but the noise, really, shits me. when sleeping is already hard enough due to topography, wind, cramped conditions etc, another factor that i can control makes sense.
over winter i spend +35 nights in tents, so it all adds up.
also, as contingency, if i puncture a down mat i will have 2 layers of nylon blus 1mm of compressed foam under me (folded into 3rds, on top of rope and pack under legs even better), which appeals more than 0.5mm of tin foil.
the drawback is you cant inflate my mouth.
the hand pump mentioned on the regular mats is sloooow (i shared a tent last weekend with a guy who had this), but the UL versions have a dry bag-pump which can work well (a bit shit inside a small tent tho).
as it goes, ive done 23 nights this winter on a down mat, in temps down to about -25c, on ice, snow, frozen soil and concrete and not had issues with cold coming thru. thats impressive i think.
the only system that beats that is 2 closed cell mats, or a closed cell + a regular thermarest. both of which take up much more space.
as yet i still cant see why an inflating mat would be punctured by anything other than a mishap. over several years of using them in winter ive yet to see it happen.
that said, i still plan for it.