haven't used it in the cold yet so I can't speak to how warm it is, but it is super comfortable. I am a 5'4" female. I purchased the small size fearing it might be uncomfortably short, but it's not. When I stretch out fully on my stomach/back my toes/heels hang jsut off the end but it's not uncomfortable. And since I sleep mainly on my side it works out perfectly. In fact, the primary reason I went with this mat was because I wanted to sleep on my side without my hips and shoulders and the ground and I'm not disappointed.
This review was written in the old system and had content requirements that are different than reviews written today.