New Swim Fin Manufacturing Technique Relies On Stevens Urethane To Streamline Process, Eliminate Expensive Molds

TPU Offers Fabrication Versatility, And High Performance Durability and Elasticity

Easthampton, Massachusetts — New Fab Force™ swim fins from Force Fin, Santa Barbara, California, incorporate a new patented manufacturing technique that relies on the performance properties of Stevens Urethane thermoplastic polyurethane sheet to speed production and improve fin performance. Fab Force™ fins offer superior snap and thrust to provide more efficient propulsion through the water. Bob Evans, president and designer, developed the new manufacturing technique that eliminates the need for expensive molds in both prototype and production.

"We are a product design company," said Evans, "and we were creating new products faster than we could make molds for production. Our challenge was to find a way to eliminate molds from the design and production process." The result is a revolutionary approach that applies soft goods techniques to hard goods production.

During product development, the company cuts sheets of Stevens Urethane film in the desired pattern, sews them together, then introduces castable polyurethane between the TPU sheets. The castable polymer bonds with the Stevens Urethane, and hardens to fill out the product and give the fin its structural form. The urethane film serves as both the mold and the outer skin or shell of the finished product. It must bond well with the internal polymer, match its elasticity, and provide a durable, high gloss outer layer.

Evans' new technique speeds and simplifies product development. This low-cost approach permits a design to be quickly prototyped and tested, modified to improve performance, then prototyped and tested again. By eliminating expensive molds, a designer can easily tweak a design to precisely achieve the desired performance. Finished products are manufactured in much the same way, with the TPU sheets radio frequency welded together rather than sewn.

"Stevens Urethane has really helped us to optimize the design process," said Susanne Chess, vice president for Force Fin. "Traditionally, you can't test the product without making a mold, which can cost thousands of dollars. Then, if it isn't quite right, you have to make a new mold, at an additional cost. Our new process is similar to the fashion industry. If it isn't what we want, we just change the pattern."

Elasticity, durability, and abrasion resistance of the materials are important to the performance of Fab Force products. The speed or snap of the rebound of a fin greatly increases its propulsive qualities. Before selecting Stevens Urethane, Evans considered and tested many other materials, including vinyl, rubber, nylon, urethane coated nylon fabrics, and vinyl coated polyester and nylon fabric. TPU was the only material that offered the necessary combination of performance properties.

"We decided upon TPU in general, and Stevens TPU specifically, for its four-way elasticity. This enables the film to expand uniformly when the castable polymers are introduced, which gives us products of consistent quality," said Chess.

Elasticity of the shell material is critical to the performance of the fin. When vinyl or fabric coated materials are used, for example, the blade is slower than when elastic materials such as TPU are used. The particular urethane film used for shaping each Fab Force model matches the rebound of the castable polyurethane used for that model. This prevents the fin from delaminating even with repeated flexing from kicking up and down. Tests have shown Stevens Urethane to retain its elasticity through 10 million 90-degree flexes, which translates to about 15,000 dives.

Chess also noted that Stevens manufactures its TPU film with superb, glossy aesthetics at the required thickness of 32-35 mil. Since the TPU remains as the outer layer of the fin, a high gloss material is important to the aesthetics of the finished product. TPU's high abrasion resistance is also important, so the fin does not pierce or tear when it comes in contact with sand, rocks, barnacles or other abrasive surfaces typically found in underwater environments.

"The quality and consistency of Stevens Urethane helps us deliver better fins, and quickly introduce new products designed for specific market niches," said Chess. "We're combating a market perception that low end plastics are quality, so it is essential that Fab Force fins are highly durable and abrasion resistant. The durability of Stevens Urethane will drive the product line’s success."

The TPU also allows Evans to use a variety of foot pocket designs and materials for the fins, in many cases a foam pocket that is very comfortable for the wearer. By contrast, injection molded fins are more limited in the type of foot pocket design, where Evans can simply RF weld or sew any type of pocket they want.

Based in Easthampton, Mass., Stevens Urethane manufactures a full range of high-performance urethanes for use in a wide variety of "can't fail" applications for consumer, medical, commercial, and industrial markets. Stevens Urethane is the only company in the world to offer urethane in blown film, extruded sheet, tubing, cord, and profile form.

For additional information, contact: Stevens Urethane, 412 Main Street, Easthampton, MA 01027. Phone: (413) 533-8100, or toll free at 1-877-TPU-FILM (1-877-878-3456). FAX: (413) 552-1195. E-mail: info@stvure.com. Stevens Urethane is a business unit of JPS Elastomerics.

Contact Susanne Chess at Bob Evans Design, 715 Kimball Avenue, Santa Barbara, California, 93103. Tel: 1-800-FIN-SWIM or (805) 966-9628. www.forcefin.com.