Scalloped outer edges creates greater surface area for water to pass over, allowing the swimmer to push more water during kicking drills and training sets.
Medial edge openings create a valve effect, in which water is captured on the underside and forced through the smaller opening. More resistance is created on the down-kick.
Channels at the top and bottom of the fins help guide water in the proper direction which helps rotate the foot into the correct orientation for maximum kick efficiency.
- via swimoutlet.com