Very comfortable and am considering getting an extra pair.  Amazingly light.  I sometimes forget I'm wearing &#34;real&#34; shoes.  The 39 is a little shorter than I normally expect from that size, so my toes are pushed up against the front.  But, it seems to stretch a little so I wouldn't want it much larger.  There really isn't a lot of specific arch support (which I usually really need as my feet tend to overpronate), but it hasn't really been a problem. I wear them to teach chemistry lab and find them comfortable.  I've bought a little arch insert but haven't needed it, yet.  Updated:  I have since added a full foot arch support that has helped.  My toe is starting to come through the front, though, but I think that the 40 would have been too wide and loose (since the 39 fits the shape of my foot if not quite the length).  The bottom is wearing away pretty quickly, too.  One MAJOR warning:  they are SLIPPERY when wet.  I have wiped out or almost wiped out several times when coming in from outside when it is wet.  Overall, I still like them, but they're not as durable as I would have liked.  (Were rated 4/5 and now are 3/5).