A Vibrant Market for Thermoplastics

An athletic shoe may contain more than 50 components. Like any composite structure, the final product is much more complex than it seems at first glance.

Presenting a paper at the American Chemical Society Rubber Division's spring technical meeting in May, Kim Ames of shoemaker Nike in Jakarta, Indonesia, said, "Thermoplastic materials account for about half of all footwear outsoles today and include thermoplastic rubber, thermoplastic polyurethane, ethylene vinyl acetate, polyvinyl chloride, and polyolefin elastomers."

Engineering and performance demands for athletic shoes are rigorous. "There isn't just an outer-sole compound for running," Ames said, there are also "compounds for training, racing, trail running, adventure racing, extreme hill running, winter running conditions, and so forth. Each compound is designed for different needs in terms of durability, traction, and weight."

Thermoplastic elastomers are attractive to producers because they are easy to process and have excellent low-temperature properties and a rubberlike look and feel and are easy to color and paint. Consumers love them because the materials offer good traction on ice and wet surfaces, and especially because of the fashion choices the materials allow. A lot of people, she said, "are wild about shoes--particularly athletic shoes, virtually all of which are made in Asia."

"There are magazines devoted just to shoe collecting," Ames said. "And if you pick up a copy of Runner's World or other sports-specific magazines, they cite specific outer-sole compounds by name for specific shoe manufacturers. They give details on weight, filler type--carbon or not, soles that do or do not leave scuff marks--and so forth," she said. Consumers, like manufacturers, "are very passionate about the product." If the shoe fits, they are more than willing to wear it--or collect it.