First Impressions

The first time I picked up a pair of Mares X-Streams, I was struck by how light they are. At about 1.5 pounds per fin, they are shockingly lightweight for a full-size performance fin. The tri-material construction uses different compounds for the foot pocket, blade, and channel inserts, and the OPB pivoting blade system looks immediately different from any fin I have used before.

After 50+ dives across destinations from Komodo legendary currents to mellow Bali muck dives, these fins have fundamentally changed how I think about fin efficiency.

OPB - Not Just Marketing

The Optimized Pivoting Blade is the defining technology of the X-Stream. The blade hinges at a specific point in the foot pocket, maintaining optimal angle throughout the entire kick cycle. Traditional fins only achieve their ideal blade angle at one instant during each kick. The OPB system keeps you in the sweet spot for both the downstroke and upstroke.

In practice, this means you generate consistent thrust with every part of the kick. In strong current at Komodo Manta Point, I was keeping up with divers on massive freediving-style fins without the same level of exertion. The difference is most noticeable on repetitive days - after four dives in strong current, my legs were less fatigued than expected.

Comfort and Foot Pocket

The riddled (perforated) foot pocket prevents the parachute effect where stagnant water creates drag resistance with each kick. Water drains through the perforations rather than being forced out. The foot pocket is soft and flexible - no fin foot after long dives. The toe area is particularly soft, almost jelly-like, which eliminates the pressure point that stiff toe pockets create.

I did upgrade to bungee straps after a few dives. The standard ABS buckles work fine but add weight and can be finicky with thick gloves. The bungee conversion makes them almost weightless on your feet and the quick-release tab is much easier to operate. This is a common mod in the diving community and Mares even offers their own bungee kit.

Propulsion and Efficiency

The X-Stream uses a unique channel design on the blade surface with longitudinal grooves that channel water flow. This reduces turbulence and cavitation at the edges of the blade, meaning more of your kick energy goes into forward motion. In practical terms, you cover more distance per kick cycle compared to solid-blade fins of similar size.

The Up-Kick (return stroke) is where these fins really stand out. Because the pivoting blade opens up on the up-kick, you actually generate meaningful thrust on the return stroke instead of just dragging the fin back. Divers who use a modified frog kick or back kick will find the X-Stream particularly responsive.

The blade material is SEBS (styrene-ethylene-butylene-styrene), a thermoplastic elastomer that offers excellent energy return. It springs back to shape aggressively, giving you that snap at the end of each kick that experienced divers look for in a performance fin.

Travel and Durability

At 1.5 pounds per fin, the X-Stream is one of the lightest full-size performance fins you can buy. They pack flat and take up minimal space in luggage. The SEBS material is resistant to UV degradation and ozone cracking, which means they do not turn to dust after a few years of tropical sun exposure like some rubber fins.

The only durability concern I have noted is the spring strap attachment point. If you use metal spring straps (recommended), the plastic attachment loops can wear over time. Some divers reinforce them with a small cable tie as preventative maintenance. After 50+ dives, mine show no signs of wear.