Even though these socks are really expensive, they're definitely high quality and fit unseen inside all of my flats-style shoes, which I wear almost daily. They also work well for fancy high heels, etc. Never thought I'd be able to wear anything besides hose under high-heels!  I'm a size 7.5-8 and they fit my feet perfectly.  I could see how they could be a little tight on a size 9, though, as I get slight indentations where the rims of the socks go around my heels.  They are very comfy, won't slip off my feet, and keep my feet separated from my shoes; no stinky feet or stinky shoes!  I'm going to buy a few more pairs since I know I'll use a pair every day.