April 1, 2005

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Uniform Variety—Working Knowledge for Tennis Balls

Service! How to manufacture tennis balls

By Mark Fischetti

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Manufacturers make more than 240 million tennis balls a year worldwide. And they are surprisingly uniform, given that they begin as natural rubber and wool, which vary with every barge and bale. To be stamped "official" in accordance with the International Tennis Federation, a ball must meet rigid specifications for deformation and bounciness. Rubber, which "varies as much as lettuce," according to Lou Gagnon, technology manager at Head/Penn Racquet Sports in Phoenix, Ariz., is combined with up to 11 chemicals to create a homogeneous slurry. The mixture is pressed into molds to form the ball's center, or core. To craft a consistent cover, wool, nylon and cotton are woven into a felt that is soaked, shrunk and dried.

Ironically, in parallel with such efforts at consistency, the core's composition and the cover's nap length and tightness are fine-tuned to create one of three speed classes of balls: fast for slow courts like clay, medium for the ubiquitous hard courts, and slow for the fast grass surfaces. U.S. players prefer a fast game and generally play on hard surfaces, so the air inside balls is pressurized to about two atmospheres to make them more responsive. Many Europeans prefer slower play, typically on softer courts, so "nonpressurized" balls, sealed at one atmosphere, are also commonly sold.

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Mark Fischetti was a senior editor at Scientific American for nearly 20 years and covered sustainability issues, including climate, environment, energy, and more. He assigned and edited feature articles and news by journalists and scientists and also wrote in those formats. He was founding managing editor of two spin-off magazines: Scientific American Mind and Scientific American Earth 3.0. His 2001 article “Drowning New Orleans” predicted the widespread disaster that a storm like Hurricane Katrina would impose on the city. Fischetti has written as a freelancer for the New York Times, Sports Illustrated, Smithsonian and many other outlets. He co-authored the book Weaving the Web with Tim Berners-Lee, inventor of the World Wide Web, which tells the real story of how the Web was created. He also co-authored The New Killer Diseases with microbiologist Elinor Levy. Fischetti has a physics degree and has twice served as Attaway Fellow in Civic Culture at Centenary College of Louisiana, which awarded him an honorary doctorate. In 2021 he received the American Geophysical Union’s Robert C. Cowen Award for Sustained Achievement in Science Journalism. He has appeared on NBC’s Meet the Press, CNN, the History Channel, NPR News and many radio stations.

More by Mark Fischetti
Scientific American Magazine Vol 292 Issue 4This article was published with the title “Uniform Variety” in Scientific American Magazine Vol. 292 No. 4 ()
doi:10.1038/scientificamerican042005-2Uwg5g1yKMjWOyakoYxIdZ
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