These fit perfectly.  I Think the trick is in getting them the exact size for your foot.  I've gone through so many but they are ususally a size 4-10. I am an 8.5 and that span won't put the slick part where it needs to be on my heel for it not to slip.  These were a smaller size span and I think that's the trick.  Also, bamboo is SOOOOO soft!