Monofin vs Bifins — Which Freediving Fin Style Gets You Deeper?

Walk into any freediving shop or browse a gear forum, and you will hit the same debate within five minutes: monofin or bifins? It is the question every intermediate freediver eventually confronts — usually right after they realize plastic snorkeling fins are costing them meters on every dive.

Here is the problem with how most people frame this debate: they treat it like a winner-take-all comparison. "Monofins are faster." "Bifins are more natural." Both statements are true — and both are useless without context. The real question is not which fin style is objectively superior. The real question is which fin style aligns with your training goals, your competition discipline, and where you are in your freediving journey.

We will answer that question by comparing every dimension that matters: propulsion mechanics, depth potential, learning curve, energy cost, and competition rules. You will leave knowing exactly which fin to buy next — and why.

Bifins vs Monofin — Quick Comparison

Before diving into the nuances, here is the high-level picture. Six dimensions where these two fin styles genuinely differ.

Bifins — The Natural Choice

Bifins are two separate fin blades, one on each foot. You propel yourself with a flutter kick — alternating leg motion, the same kicking pattern humans have used in water since we first learned to swim. That familiarity is bifins' greatest strength and their most overlooked advantage.

Because the flutter kick is intuitive, your brain does not need to allocate conscious attention to fin technique during a dive. That freed-up mental bandwidth goes toward equalization, body position, and relaxation — the three variables that actually determine depth for 95% of freedivers. You are not fighting your equipment while you are fighting the urge to breathe.

Why Bifins Dominate Training and CWTB

Bifins are the official fin of CWTB (Constant Weight Bifins), a discipline recognized by both AIDA and CMAS. CWTB has grown rapidly in participation over the last five years because it lowers the barrier to competitive depth freediving. You do not need to learn dolphin kick. You show up, put on bifins, and compete with the kick you already know.

For recreational and training use, bifins are unmatched in versatility:

• Pool dynamic training: Bifins let you focus on CO2 tolerance and streamlining without also managing a new kick pattern.
• Depth adaptation: When you are still learning to equalize at 20m, 30m, 40m, the last thing you need is a fin that demands your full attention. Bifins fade into the background — exactly where they should be.
• Safety and buddying: Bifins offer superior maneuverability. If your buddy has a problem at depth, you can turn, reposition, and assist faster with bifins than with a monofin.

Monofin — The Efficiency Weapon

A monofin is a single large blade that holds both feet together. You propel yourself with a dolphin kick — a full-body undulation that starts at the shoulders, travels through the core, and exits through the fin blade. When executed correctly, this motion converts nearly 100% of your muscular output into forward thrust with minimal hydrodynamic loss.

That is the physics. The human reality is more complicated.

The dolphin kick is not natural. It requires core strength, thoracic spine mobility, and ankle flexibility that most people do not have out of the box. Your first session in a monofin will feel awkward. Your second session will feel slightly less awkward. Around session six or seven, something clicks — your body discovers the undulation rhythm, the fin stops fighting you, and suddenly you are gliding through 50m of dynamic with noticeably less effort than bifins.

That moment is when a monofin earns its price tag.

Why Monofins Rule CWT Competition

CWT (Constant Weight) with monofin is the deepest freediving discipline in the world. Current CWT world records sit over 130 meters — consistently deeper than CWTB records. The physics is simple: a single oscillating foil blade generates less turbulence at the edges than two separate blades. Less turbulence equals less drag. Less drag equals more depth for the same oxygen investment.

For competitive freedivers targeting national records or podium finishes, a monofin is not optional. The 8–15% depth advantage at elite levels is the difference between a medal and watching from the sidelines.

• Hydrodynamic efficiency: Energy return can exceed 90% on high-quality carbon layups. Each kick cycle converts almost all your effort into forward motion.
• Speed-to-depth advantage: Faster descent means you spend less time at depth consuming oxygen. At 60m+, every second matters.
• Streamlining bonus: Feet together, single blade — your frontal cross-section is smaller, further reducing drag.

Three Freedivers Who Should Choose Bifins

Three Freedivers Who Should Choose a Monofin

How Much Depth Does a Monofin Actually Add?

This is the question everyone really wants answered. The honest answer: it depends on your technique.

At the elite level — where dolphin kick technique is near-perfect — CWT monofin records consistently exceed CWTB bifins records by 8–15%. For a 100-meter diver, that is an additional 8–15 meters. For a 40-meter recreational freediver with average dolphin kick, the gap shrinks to 3–8% — and can even go negative if your monofin form is poor.