I ordered these for my husband who suffers from neuropathy caused by diabetes.  His feet never seem to be warm enough.  He wears a 10 1/2 men's shoe, so I ordered an XL, the largest available size.  They were too small and tight.  The stitching across the top of the foot made them even tighter.  I would have preferred an exchange, but since there was no larger size, we have ordered a different brand of down slipper for him.  I will say this seller was very prompt in responding to our request to return the slippers, and for that I am grateful.  However, they do not cover return postage.  If there had been a shoe size associated with the S,M,L,XL sizes, it would have been easier to tell they weren't going to fit.