These seemed to run a little small.  I'm normally a 9 or 9 1/2 and the large just fits.  I was a little worried about the low back on these, but they hug my heel perfectly.

These slippers keep my feet very warm but not at all sweaty.  I can't really tell how warm until I take them off and feel the cold of the house.  The bottoms are slightly tacky, so if you have a dog, expect to see some nastiness on the bottoms for the first week or so of wearing (it wears off fairly quickly thankfully).

I will buy these again, and also I've purchased more as gifts.