"Buying them online is a horrible idea!!! Each pair is handmade, and no two clogs are exactly the same size. When I bought mine a few months ago in the store, I had to try on 6 different pair in the same size to find a good fit. But, if you do insist on buying them online... The back of the pro is a false back - which means it should NOT hug your heel - the back should fit loose, and your heel is supposed to slip up and down as you walk. It is weird at first, but after a few days of wearing them you won't even notice. The arch is HIGH. Like crazy high. Again, that is the way they are supposed to fit. It takes a few days to get used to - then it feels awesome! "