The TwinJet swim fin shown during downstroke. The process is repeated during upstroke.

Key to this design is its dual-blade made from tough, yet flexible, Monprene thermoplastic elastomer from QST Inc., part of Teknor Apex's Thermoplastic Elastomers Div., St. Albans, Vt. According to ScubaPro, the dual blade converts more of the diver's kicking energy into forward motion than conventional paddle-shaped swim fins. Each kick with a typical fin creates turbulence that wastes energy, says the company. With the Twin Jet, however, displaced water flows over the top and bottom of each blade, producing a pressure differential, similar to that which generates lift in an aircraft wing. But instead of lift, it creates forward motion.

Because the fin must flex smoothly as a diver's foot cycles from downstroke to upstroke and back, ScubaPro needed a tough, elastic material that would not only snap back to its original position at the end of each stroke but also resist tearing after constant flexing.

In conventional swim fins, resilience or "snap" is typically provided by natural rubber formulations, but these materials don't sufficiently resist outdoor weathering, say company officials. Synthetic rubber materials, such as EPDM, and many types of TPE can withstand outdoor elements but don't provide enough "snap." Monprene TPEs, on the other hand, are said to be resilient, offering high tensile and tear strength combined with good weathering resistance. Further, Monprene TPEs have a low coefficient of friction, which contributes to low drag in water.

The new concept fin includes other special features that will have divers kicking easily. For instance, vents let water flow through after it passes over the twin blades, while the fin's angular configuration is said to maintain symmetry between upstroke and downstroke. According to ScubaPro, these combined features help reduce diver fatigue and cut air consumption by as much as 40% compared to conventional swim fins.

ScubaPro also offers a special diving fin called the Twin Jet Graphite molded of a softer, more flexible Monprene formulation that is lighter in water than the standard Twin Jet.