Nuts and Bolts, 8/27: “The Extrudables”

by: Justin diFeliciantonio | August 27, 2012

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Daily dispatches on gear from the U.S. Open.

Jamie Hamptonextrude |ik?stro?od| verb [with obj.] (usu. be extruded). To thrust or force out: Lava was being extruded from the volcano. To shape (a material such as metal or plastic) by forcing it through a die.

—New Oxford American Dictionary


NEW YORK—All around the grounds, central to the grunts and thwacks and cheers, on match and practice courts alike, is a polymer. Tecnifibre, Luxilon, Kirschbaum—it’s sharp and stiff and ships in coils from Belgium and Korea and China, in a myriad of edged and -agonal shapes. The stuff caught fire on tour in the early oughties, and while the old guard has execrated its influence, there’s no going back. For better or worse, it’s changed the way the game is played.

We’re talking about polyester string, of course. And as you must by now know, it’s in the racquets of practically every pro in this tournament, because of its ability to project the ball over the net with unparalleled power, spin, and control. (As former pro Cecil Mamiit told me yesterday, “It just makes the ball dance.”)

But for all the chatter about poly’s performance-enhancing qualities, its manufacture remains, in the minds of most, mystifying and obscure. I mean, really, how does this stuff come to be? One answer: Extrusion.

“This is a crude analogy, but think of it like this,” explains KT Kim, who works as a director at Solinco, a South Korean-based string company. “You put it into a melting pot. You get all the polyester, you put whatever chemicals you want in it, and melt it down into a goo. Then you extrude it through something like a Play-Doh press. Remember Play-Doh? Where you could make the shapes? So you extrude it into your desired shape. And then, you pull the material down into several cooling and heating baths, which harden the string into its final shape. Finally, you wind it up.”

The extrusion is key. Because the string’s properties, and thus performance, depends largely on variables present during the process—i.e., how quickly the material is extruded; and how long, to what temperature, and how frequently it’s cooled (and then re-heated).

As a matter of course, the finer details of a poly’s make-up are proprietary; every company has its magic dust. But out on-court, its effects are clear: Extrusile projectiles are flying everywhere.

For more on strings, please see:

Part one of our interview with Solinco's KT Kim
Part two of our interview with Solinco's KT Kim

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