This 6mm boot has a very thick , tough running shoe sole that is excellent for walking on rocky, tough, sharp surfaces. It is also very hard to find proper fitting strapped fins with this size of a shoe. Most fins do not come in X-Small and even those that do, still might be too big. This bigger boot will totally help with that and make an X-Small strapped fin fit beautifully. This boot fits a size ladies 5-6 shoe.