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There are nine major characteristics in a surf fin: material, base, depth, sweep, area, cant, toe,foil and flexibility. That's why surfers should pick fins carefully by adjusting their surfboard to their experience in wave riding.

Molded fins are the most common kits available in the market. They often are seen as custom fins and come with the usual surfboards sold in a surf shop. There's also the resin transfer molded (RTM) fin, a high tech unit designed with aerospace-based concepts. The RTM has a layer of honeycomb foam. The fiber glass fin has a stiff base and a certain amount of tip flex.

Surf fins can be stiffer or more flexible. The most resistant fins ensure more driveability while a softer kit is provides more safety. They can be inserted in a wider or narrower base, in the surfboard fin box, depending on your speed/drive preferences.

Shorts fins are great for "slide surfing" because there's less friction in the water. Longer fins may avoid wipe outs, but will also slow your wave rides. If the overall fin area (base plus depth) is bigger it will be harder to turn and carve.

The sweep of a fin is very relevant, too. If your fins are strongly angled backwards, your bottom turns and cut backs will be more rounded. With the cant angle of a fin you may determine the responsiveness of your surfboard - decreasing the cant will ride you faster in a straight wave line.

The toe angle is the angle relation to the stringer. It can be angled inward or not. If the front of the fins is closer to the stringer, making an inverted "V", any slightest body balance will get a response by the surfboard.

Finally, look for the importance of the foil. Like in an aircraft wing, you can get curved or foiled fins. In hydrodynamics, the more pronounced the foil, the slower you'll surf a wave and a lift will be created under the surfboard. In the next chapter, we'll learn what are the best surfboard fins in the world for your level of surfing.