Tried the boots on as soon as I received them.  Based on previous reviews, I put on a light weight sock to start with.  My foot slipped in without too much trouble.  Now I will try to increase the thickness of my socks until the opening is stretched enough to handle the thickness of the socks I wear the most.  This boot is extremely well made; I am very happy with this purchase.  I love Keen products and these boots are no exception.