Stretchy straps ensure a good fit. Not a great buy. My old original airweave pads were looking a bit tatty so I thought I would try these, trying to avoid leather ones (which I know get super hot) I spotted the gel ones thinking they would be a nice comfy compromise. ) and the arch was so high that foot was sliding over to the outside of the slipper, so hurting. However, it appears to be the correct size (US 9, European 42) that is his shoe size, and since the leather laces allow the wearer to loosen or tighten the fit somewhat, I expect they will fit him just fine. I have purchased TWO pairs in the past SIX months and both developed a big toe hole after THREE months of use! I am not going to the trouble of finding out so will be returning them for a refund. Its a shame because he walks so well in them but as soon as I pick him up they fall off. I will buy from this seller again in the future. I anticipated this, it?s just the nature TPU plastic, and don?t mind coming back to order more.