I wear a size 13 and require excellent arch support and plenty of toe room, so I have great difficulty finding comfortable shoes.  When I put these shoes on, I almost wept for joy because they were so comfortable.  The footbed molded perfectly to my foot, and there was ample room in the toe box. Unfortunately, as soon as I walked in them the shoe slipped off my heel with every step.  I tried heavier socks, but that didn't help.  I think the problem is that the back of the shoe goes straight up instead of curving slightly.  Sadly there is no such thing as a size 12 and a half, so I will have to return rather than exchange.