Understanding Fin Stiffness for Freediving

If you ask a dive buddy, there are all sorts of different things they might say about fin stiffness, but don’t let all of the different stiffness ideas of fins intimidate you when you’re buying your first pair of carbon or fiberglass fins. The stiffness of your fins matters, and is always decided in accordance with body weight. There are a couple of different schools of thought on this, which will be summarized here.

The Traditional Way

The traditional way of choosing stiffness is a calculation of pure bodyweight, regardless of what activity you’e doing.

Soft = 100-155lbs

Medium Soft = 155-200lbs

Medium = 200 - 255lbs

Hard = >255lbs

This is the way that we select stiffness for new customers in the shop, and the base for thinking about fin stiffness that you will see in most shops. The thing to remember is that some fin manufacturers call “hard” what would be a medium or soft at most shops and vice versa, so if possible be sure to look at reviews or go into a shop to feel the fins yourself. Softer fins are also a lot better for people with knee or ankle injuries, because they put less strain on your joints.

Spearfishing Focus

There is another way of thinking about fin stiffness that some say is better for spearfishing because it takes into account the kinds of activity spearos specifically face. This school of thought argues that because spearos have to fight fish, kick off the bottom, and battle current, that a stiffer fin (about one category above where you’d normally be) is better. The downside to this is that stiffer fins more generally exacerbate inefficiencies in your kick form, and if you haven’t learned to kick slower with stiffer fins they will also drastically shorten your dive time and use up more oxygen. For divers taking tons of dives in a single day of diving, those factors can lead to worn out legs and end the day early, but for divers that are only taking a few drops a day for big fish, this philosophy makes a lot sense.

However, Neptonics co-founder Jerry Guerra is known for using ultra-stiff Neptonics G.F.T. Agguato fins even when his body weight would call for a medium stiffness according to both of the other schools. This is not a philosophy for the weak-legged or lighthearted. The rationale behind it is an extreme version of the spearfishing emphasis: the extra stiffness is absolutely essential for being able to kick off the bottom, put pressure on a fish when needed, or maneuver in the ripping currents of east Africa. The downside to extra-stiff fins is that any inefficiencies in your kick form will be felt exponentially worse with a less forgiving fin. The only reason this particular philosophy works for Jerry is that he is confident that because of his 20+ years of freediving, he has mastered kick form with minimal inefficiencies so they won’t be made worse by extra stiffness.  This is not a recommended way to buy a set of fins for pretty much anyone but Jerry, but was included to demonstrate further the pros and cons of increased stiffness.

We hope this article helped you navigate the wide world of freediving fins, and if you have any questions for the shop, feel free to call us at +1-813-867-3250!