Been making fins for lots of Great shapers over the years and have came across a closed cell material that bindes with resin and glass that lets the dislogded fin to float back to the beach can be glass-on or fin system and looks bloody nice as current core fabrics.
As a shaper, fins always worried me a lot. Wood, fiberglass, plastics, composites, glass on or changeable ones, whatever they are made, all fins had a problem in common: wheight. If they can float, maybe two problems are in way to be solved. Good luck in your research.
Wood always floats, I’ve had a couple of fins I’ve made float up on the beach, makes a good converstain starter for the person that picks it up for you as you slew sideways on your board on your way in trying to find it…