I've used my "old" yellow NeoAir in temps down to zero. Used by itself, I found that it started feeling cold in the 25-30 degree range (and I'm not a particularly cold sleeper.) With a Z-Lite pad under it, it was fine down to 10 or lower. My experience at zero was unintentional (temps dropped a bit lower than predicted); I was using the Z-lite and NeoAir with a 20 degree WM bag and wearing WM Flash pants and jacket in the bag, but started to feel cold underneath around 5am (I'd estimate temp was 0 - 5 at that point.) I also had a nylon footprint under the Hubba tent.

I recently took my NeoAir All-Season into 20-degree temperatures (it may have gotten into the mid to lower teens one night.) I was using the same bag, without the down pants or jacket, inside a Carbon Reflex tent, with a footprint. Not only did I never feel cold, I could definitely feel heat radiating back to me. When you first lay down, or when you shift position, you'll feel a cold spot for about 30 seconds, until that part of the pad "warms up." Then it's positively toasty.

If I were choosing one NeoAir pad to fit all my trips (Ohio-Kentucky-Indiana, very little snow camping, a couple of cold-weather one or two night trips each year) it would be the NeoAir All Season. It seems a very good compromise between weight and warmth - there's only a 4-ounce difference between the 66" regular and All-Season. Remember, I said I'm a "normal" sleeper, not a "cold" sleeper. (My second choice would be an Exped Downmat 7, especially if I was regularly camping in 0 - 20 temps. Much higher R-rating, but it also weighs nearly 2 pounds. The NeoAir replaced it for my own winter use.)