Well, this is my theory on why you might experience nasty blisters on the heels of two boots: Nike AZT 90 III and Nike Vapor I/II. First, I'd like to start off by saying that it's normal to experience a blister or two when breaking any boots in, however, I noticed as I was cleaning the AZT 90 IIIs that the heel was creased near the achilles (ex. Vapor I/II). You can see and feel the material expand near the crease (~heel) and this causes uncessary friction. I've been playing in pulses for a couple months and last week I used my AZT 90 IIIs in a pick-up game and it gave me some nasty blisters, one the size of a quarter on my right heel (right footed) and one the size of a dime on my left. This happened to me with the vapors as well. It wasn't as bad with the vapors as my heel had callous'. (The heel on 95% boots are constructed with a U back) I'd like to point out I didn't use these boots since January and my heels probably softened up, but nonetheless it has been a painful experience.