String Theory: The synthetic revolution that changed tennis forever.

The last Grand Slam of the tennis calendar kicks off today in Queens, New York.  And while the likes of Roger Federer, Rafael Nadal, and Serena Williams will all be missing due to injury, the newest generation of top tennis players will still be hitting the hard courts in USTA Billie Jean King Tennis Center for the U.S. Open. Spectators in attendance and watching at home will be treated to men and women hitting tennis balls at absurd speeds and with spin unimaginable 50 years ago. Today’s game bears only a passing resemblance to the finesse game…

While there’s little doubt that, on average, athletes today are better trained and conditioned than in the past, they aren’t necessarily better athletes or tennis players, for that matter. Advances in materials technology have allowed for larger racquet heads and have tripled the size of sweet spots. This has freed players to swing harder and freer. Yet, the most significant change between modern tennis and the game dominated by the likes of Rod Laver, Margaret Court, Jimmy Connors, and Martina Navratilova are the strings available to competitive and recreational players. 

The arrival of polyester tennis strings during the 1990s changed the sport. A Flemish company named Luxilon Industries released the Big Banger in 1991 and the Big Banger ALU Power in 1994. For a few years, the strings sort of floated under the radar. It wasn’t until 1997 when an unheralded Gustavo “Guga” Kuerten stormed to a French Open championship, defeating two former champions in the process, that the new types of strings burst into prominence.

Polyester strings allowed Kuerten to swing harder at the ball, generating more topspin, while still keeping his shots inside the court. Shots that would have hit the fence with natural gut strings or nylon strings now traveled with precision and power. That famous looping backhand Kuerten rode to the top of the ATP rankings never would have been possible. The rest, as they say, is history. The professional game would never be the same.

The primary material used in polyester strings is a thermoplastic polymer resin called polyethylene teraphthalate (PET). It is fairly common and used in everything from clothing to water bottles. As a textile, PET normally goes by the more familiar name, polyester. PET consists of polymerized units of the monomer ethylene terephthalate, with repeating (C10H8O4) units. PET is commonly recycled, and has the number “1” as its resin identification code (RIC).

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PET was patented in 1941 by John Rex Whinfield, James Tennant Dickson and their employer the Calico Printers’ Association of Manchester, England. E. I. DuPont de Nemours in Delaware, United States, first used the trademark Mylar in June 1951 and received registration of it in 1952. It is still the best-known name used for polyester film. The current owner of the trademark is DuPont Teijin Films US, a partnership with a Japanese company.

Polyethylene teraphthalate (PET)
Polyethylene teraphthalate (PET)

According to Tennis Industry Magazine, manufacturing polyester strings involves a five step process: Selecting the raw materials and other ingredients; Creating the filaments from which strings are made; Multifilament construction; Coating and sizing (in the case of multifilaments); and Post-processing, if any. (For a more detailed description of the process, visit Tennis Industry Magazine.) 

The secret behind polyester string’s success is that it offers very little power. It is a very stiff string. (As a rule of thumb, tighter strings increase control at the expense of power while looser strings increase power at the expense of control.) Counterintuitively, this allows players to hit for more power since they are able to swing harder and faster at the ball. This, in turn, allows more topspin to be generated which further adds to the ability to keep the ball in play. Moreover, polyester strings are smoother, more durable, and snap back into place quicker than other types of string. This so-called snapback effect further adds to the generation of topspin. In short, for most hard-swinging professional tennis players, using polyester strings is a win-win-win situation. Players that do not incorporate such violent swings tend to use a combination of polyester and natural gut/nylon strings.

A quick look at this slightly dated table from Tennis Companion shows the strings used by some of the world’s top players,

RacquetTension Range
Roger FedererMain: Wilson Natural Gut | Cross: Luxilon Alu Power Rough
Novak DjokovicMain: Babolat VS Team | Cross: Luxilon Alu Power Rough
Rafael NadalMain: Babolat RPM Blast | Cross: Babolat RPM Blast
Andy MurrayMain: Luxilon Alu Power Rough | Cross: Babolat VS Touch
J. Martin del PotroMain: Luxilon Alu Power | Cross: Luxilon Alu Power
John IsnerMain: Wilson Natural Gut | Cross: Tecnifibre Pro RedCode
Nick KyrgiosMain: Wilson Natural Gut | Cross: Yonex Poly Tour Pro
Richard GasquetMain: Luxilon Big Banger Original | Cross: Luxilon Big Banger Original
Serena WilliamsMain: Luxilon 4G | Cross: Luxilon 4G
Venus WilliamsMain: Luxilon 4G | Cross: Luxilon 4G
Simona HalepMain: Luxilon Alu Power | Cross: Luxilon Alu Power
Angelique KerberMain: Yonex Poly Tour Fire | Cross: Yonex Poly Tour Fire
Caroline WozniackiMain: Babolat RPM Dual | Cross: Babolat VS Touch
Sabine LisickiMain: Yonex Poly Tour Spin | Cross: Prince Natural Gut
Johanna KontaMain: Babolat VS Touch } Cross: Babolat RPM Blast
Petra KvitovaMain: Luxilon Alu Power | Cross: Luxilon Alu Power

Running through the list, a clear pattern emerges, consistent with what we discussed earlier. Rafael Nadal, Juan Martin del Potro, Richard Gasquet, Serena Williams, Venus Williams, Simona Halep, and Petra Kvitova are all power players. Their groundstrokes are among the heaviest on the tour. Meanwhile, players like Roger Federer, Novak Djokovic, Caroline Wozniaki, and Sabine Lisicki, whose games do not involve blasting opponents off the court, adopt mixtures of polyester and a different type of string, presumably to generate a little more power than normal while not having to expend so much energy on every stroke.

So while it may appear as if tennis has not undergone any significant change, it turns out that it may be one of the sports most altered by advances in science. Who would have thought that it would be the humble racquet string that would revolutionize tennis?

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