Whatever it is, this is a bit too small for a size 9, and a bit narrow, as well.  Not surprised, though.  I'd say the manufacturer does't allow for wearing socks, especially thicker socks, with the shoe.  Easy to walk in even if it is a bit too small.  I'm going to wear it around for a while and put up with the discomfort of being too tight, just to see if the fabric material loosens up a bit and the fit becomes more bearable, but I have serious doubts about that working out.  I bought these because I thought they would be more comfortable and faster to put on than my usual lace-up boots.  It just shows how things can be deceptive at first glance.  Unfortunately, the list of sizes I saw didn't show any half-sizes being offered and a size 10 is typically too big for me.  I'll need to find a local shoe store that carries these and try a larger size.

Edited: Now, after I've had these a week or so, I see that the listed sizes now include half-sizes, which weren't there when I ordered these.  I've been wearing these every day for as long as I can stand the tightness, but they haven't changed at all.  Like others have said, they are good to walk in and have a lot of cushion added so they provide a very smooth step.  It's easy to see why people like these.