The bottom part, the dark park in the picture, doesn't stretch at all. The top parts don't stretch much either because the inner lining is fleece. Perhaps you should go with the larger size. I wear mine with thick socks underneath, and I'm sure they save on my heating bill. I like them.
These were bought as a gift that I haven't given yet so I am unable to answer the question yet.
Not to stretchy, I ordered a large and they are fine, I'm an 8 1/2