Adjustable or open-heel scuba diving fins require dive boots or socks. They fit a wider variety of feet than full-foot fins. More suitable than full-foot fins for a variety of diving conditions - because they're adjustable, you can wear different thicknesses of dive boots or fin socks to keep your toes toasty. Some divers experience improvements in propulsion with adjustable fins - in our opinion, the jury's still out on that.