The Dorsal's D1 Keel Twin Fins are a classic keel fin design. The Honeycomb material with the iconic wood inlay give the D1 a medium flex pattern and the big old-school template generates rail-to-rail speed down the line and provides hold through direction changes. The D1 Keel is the iconic match up with your retro-fish. Features Size: Fit To Board Fins in set: 2 Material: Honeycomb Tech Specs Side Fins: Height: 5.01 in Base: 6.64 in Area: 25.55 sq in HONEYCOMB: A lightweight core gives these fins the feel of glass-ons. Engineered with a medium flex pattern stiffer than Carbon Series but more flexible than Fiberglass. FFT Foil: FFT foiled fins break free sooner and are better at controlling speed. Often surfers prefer them in fast powerful surf where they do not need to create additional speed. If you have muscle memory from riding glass-ons flat foiled fins will feel the closest.