Choosing Your Fins

Written by Fin + Forage’s Andrew Miller

Fins might be the most iconic pieces of gear in freedive spearfishing. To outsiders, the long blades we carry are the most obvious signal that sets us apart from SCUBA divers, snorkelers, and tourists on the beach. To us, our fins help us to get to the bottom, retrieve fish, and effectively navigate the currents of the open ocean. No matter where you dive or how you hunt—tropics or cold water, wetsuit or no wetsuit, speargun or pole spear—fins are an indispensable part of a spearo’s kit.

With so many different choices on the market, choosing your first set of freediving fins can be an intimidating process. But it doesn’t need to be. The purpose of this guide is to help you understand what different fin features do, how those features impact your diving, and how to select a fin that will give you the best possible performance within your budget.

Why Freediving Fins?

One question a lot of new divers ask is whether they need to invest in a dedicated pair of freediving fins. The short answer is no. SCUBA fins, snorkeling fins, and even body surfing fins will all increase the power of your kick cycle and help you cover distance and depth under water. If you already have a set of fins, or if cheap snorkeling fins are the only option in your budget, you can absolutely get in the water and start spearing fish with what you have. But none of these fins are optimal for the job, and given the choice, a dedicated pair of freediving fins will help make your diving more efficient and enjoyable.

SCUBA fins, snorkeling fins, and body surfing fins generally operate like paddles. Short and stubby, they displace water in the exact same way your bare foot does, but over a much greater surface area. By moving more water with each kick, you propel yourself proportionately further than you would without fins.

The problem is that the bigger the paddle, the more energy you need to put into the fin to make it move. And when you are holding your breath under water, you have a limited amount of energy to work with, not to mention that your legs tend to use up to 60% of your oxygen supply. SCUBA fins and snorkeling fins are also often made with soft or open-heel foot pockets. These allow your foot to bend away from the fin blade at the start of your kick, reducing the amount of energy you actually transfer to the blade. As a result, you end up putting a lot of energy into each kick for relatively little in return.

A freediving fin, by comparison, operates more like a hydrofoil. As the fin flexes, the relative velocities of the water in front of and behind the fin create “lift”—similar to an airplane wing—and that force pushes the diver forwards. Because the diver only needs to deform the fin blade—rather than displace water—the fin does a lot of work with very little energy expended. In order to ensure that as much energy as possible is transferred into the fin blade, quality freediving fins have stiffer, closed-heel foot pockets that keep your foot in contact with the blade. This combination allows you to move further with less oxygen consumption and, as a result, to stay down longer.

Finally, most freediving fins—excepting the ultra-low-end and ultra-high-end models—have interchangeable blades. This means you can take your blades out of the foot pockets for travel or to upgrade to a better blade as you progress in your diving career.

What Makes a Good Spearfishing Fin?

Like most things in life, finding a good spearfishing fin is a balancing act. While freediving fins provide a good starting point, not all freediving fins are created equal.

Line diving fins (those targeted to competitive freedivers) are generally the most efficient fins on the market. These fins use the full length of the blade to create the hydrofoil shape, which in turn allows divers to get the maximum work out of the fins for the minimum amount of energy expended. These fins tend to be softer (easier to bend) than spearfishing fins because the entire benefit comes from the diver’s ability to deform the blade. The easier that is, the better the fin works.

The downside to line diving fins is that they generally have no backbone to kick into. Once you’ve deformed the blade, it is impossible to get any additional work out of the fins. In fact, if you kick a line diving fin too hard (“kick through” the fin), you actually lose energy because the blade can no longer retain its hydrofoil shape. Divers analogize these fins to biking in first gear. It is very easy to get moving and you can keep going for a long time, but if you have to fight a current or carry a lot of weight (for example, carrying a fish up from depth), it’s going to be a long, slow process.

Spearfishing fins function more like a hybrid of paddle fins and line diving fins. The base of the blade near the toes is stiffer and provides paddle propulsion, while the tip of the blade deforms into a hydrofoil. This combination dramatically increases a diver’s efficiency while also providing enough backbone to translate harder kicks into forward motion. For this reason, spearfishing fins are generally preferred for diving in currents or anywhere heavy lifting might be required.

Unfortunately, brands tend not to market fins as line diving- or spearfishing-specific. Because there is such an overlap between the freediving and spearfishing communities, and because so much boils down to personal preference, fins are often lumped together as “freediving fins.” Fortunately, there is an easy way to tell what a particular set of fins is designed for. When you pick up a blade (just the blade—no foot pocket) and bend it, a bend towards the middle of the blade typically indicates a line diving fin. By contrast, a bend toward the tip of the blade—often referred to as a progressive flex—is more indicative of a spearfishing blade.

Fin Stiffness

Freediving fins come in a variety of strengths to suit different divers and their needs. Most brands label their fins with a stiffness scale (either soft/medium/large or some combination of numbers), although it is important to note that there is no industry standard and one brand’s “soft” can easily be another brand’s “medium.”

As a rule of thumb, softer blades will be more efficient than stiffer ones because it is easier to deform a soft blade into a hydrofoil shape. However, because soft blades are easier to deform, it is also easier to kick through them. Divers with stronger legs will therefore often prefer a stiffer fin than divers with skinny legs or lazy kicks.

Which stiffness will work best for you is largely a matter of personal preference that will depend on your kicking style, your body type, and where and how you intend to hunt. That said, in recent years the trend has been for divers to adopt softer and softer fins. We generally recommend that new divers start somewhere in the soft- to medium-stiffness range.

Choosing the Right Foot Pocket

If freediving fins were a rock band, foot pockets would be the bassist. They aren’t glamorous and they won’t catch your attention at the dive shop, but a set of foot pockets can make or break a pair of fins. For this reason, we recommend that you start your fin selection with the foot pockets. Once you find a set that works for you, then you can find blades that work with them.

First, and most obviously, a foot pocket should fit and be comfortable. If the pocket is too narrow or has hot spots, you could ruin your dive with a bad case of blisters (for this reason we also recommend you use fin socks, even in warm water). If the pocket is too wide and sloshes around on your foot, you won’t transfer energy efficiently and get the most out of your fins. Ideally, a pocket should be stiff along the full length of the sole, soft around the ankles, and stiff across the top of your foot. This will give you the maximum possible power transfer without digging into your ankles.

Second, a foot pocket should have tendons that work with the blades you want. Tendons are the long protrusions on either side of the foot pocket that hold the blade in place. Some models, like the Mares Razor, have thick tendons that stiffen the back of the blade and can transform a “mid-flex” line diving fin into a more progressive spearfishing fin. Others, like the Pathos Fireblades, have skinny little tendons designed so that the blade can do as much of the work as possible. Still yet other manufacturers—notably Cetma and Alemanni—have abandoned tendons altogether.

To a certain degree, it is possible to change the behavior of a blade by pairing with a specific set of tendons. However, it is important to note that most fin manufacturers design blades with particular foot pockets in mind. It is possible to find a blade and tendon combination that change the bend of a blade so much that you can actually snap the blade in normal use. While this is unlikely, it is important to remember that not all blade and foot pocket combinations will work together.

Blade Material

Blade material is the final and most contentious part of the freediving fin equation. Most blades on the market are made of plastic, fiberglass, or carbon fiber. As a general rule, plastic fins will be the cheapest and least efficient option. That is not to say that plastic fins are bad—plenty of respected freedivers take them to 100 feet and beyond—but because they are slow to rebound, you have to put in more work at the end of each kick to change the shape of the blade in the other direction. For this reason, it is rare to find plastic blades for sale by themselves. Instead, they are often sold paired with interchangeable foot pockets to allow new divers to get into the sport at a lower price point—often $100 - $175 for a “full set” (pockets and blades) of fins.

Fiberglass fins rebound significantly faster than plastic and represent a tremendous jump in performance. They are constructed out of thin sheets of fiberglass cloth bonded together with epoxy resin. The result is a durable, smooth-bending fin blade at a relatively affordable cost. Fiberglass fins start around $150 for a set of blades and can be screwed or glued into a variety of foot pockets.

Carbon fiber is generally considered the best material for freediving fins due to its quick responsiveness and light weight. Although first generation carbon fiber fins were extremely delicate, manufacturing processes have come a long way. Quality carbon fiber fins offer extreme performance and durability at a premium price. Expect to pay $300 - $500 for a set of blades and another $150 for foot pockets. Most divers agree that unlike the jump from plastic to fiberglass fins, the performance gained from shifting from fiberglass to carbon fiber is subtle. Nevertheless, the benefit is significant enough—especially with softer fins—that most experienced freedivers prefer carbon fiber.

As with anything, there are exceptions to these rules. DiveR and Molchanovs, for example, build high-end fiberglass fins than many divers consider comparable to high-end carbon fiber fins. Similarly, the market is full of cheap carbon fiber and carbon-fiberglass-blend fins that offer marginal performance benefits over pure fiberglass.

For new divers, the most important factor when considering fin materials is budget. If you don’t have a lot to spend or if you aren’t sure you will stick with the sport, a quality set of plastic fins will do everything you need them to do. However, if you have the budget and you are more serious about the sport, a decent set of fiberglass or carbon fins can certainly give you an edge.

As with most things, what fins are best for you ultimately comes down to personal preference. Once you find a set that works for your style of diving, is comfortable on your feet, and fits your budget, don’t hesitate—just get in the water!

Find fins at https://www.odysseyfreediving.com/