My experience in cold weather was limited to a couple of weeks at the end of my PCT adventure. Admittedly, the top of the NeoAir felt cold to the touch on several of those nights, but was much warmer than lying on the ground. My hiking partners used other pads that were fairly worn and they suffered accordingly. I wore an excess of clothing in a very good bag and stayed warm. I am sure if I had another pad to put underneath the NeoAir, performance could have been significantly improved.
The NeoAir seemed to hold up in the cold just fine – although I did harbor a bit of concern with unfolding/refolding it repeatedly in the cold. I didn’t notice any ill-effects, but please note, this spate of cold weather came during the final weeks of our adventure. Had we been in-and-out of cold weather for a longer period of time, perhaps I’d have more definitive results.
Crystallization from your breath is a concern – I am uncertain how it would perform over time, especially in cold temps for weeks on end.. I wish I had better information for you, but I am afraid I do not.
The hole in the top of the NeoAir was definitely a result of my pen. I brought a Thermarest patch kit with me and performed a repair in the field that held up very nicely thus far (about three weeks of use).
The repair was rather straightforward – what wasn’t as easy was finding the leak (had to submerge in water, which is a bit of a trick. Even with it submerged I had to jostle it around for a while until I isolated and marked the leak).
I also should note that I slept in a UL tent with a Gossamer Gear polycro ground sheet for most of the trip before switching to the more substantial MSR Hubba for the final 500 miles. This obviously offered additional protection to the bottom of the NeoAir.
Again, I’d be really interested in seeing how these pads hold up over time in cold weather. Performance was to me, acceptable, but again, I carried a bag made for cold weather and wore a good deal of clothing.