Why Are Tennis Balls Fuzzy?

Tennis fans might sometimes wonder what pros are doing when they stop to inspect a new ball before putting it into play. Are they stalling to contemplate strategy? Checking the manufacturer? Paranoid about sabotage?

None of the above. They’re staring intently at the fuzz.

Unlike basketballs, footballs, and soccer balls, tennis balls come adorned with a fuzzy exterior. These tufts serve—no pun intended—a crucial purpose, one that players are mindful of when a game or even a career is on the line.

Strictly speaking, the fuzz on tennis balls isn’t referred to as fuzz. It’s known as the nap, a covering added to a pressurized rubber ball during the manufacturing process. (The nap actually comes in two pieces, giving the ball its familiar seams.) Made of wool, nylon, cotton, or a blend of all of them, the nap increases the aerodynamic drag on the surface of the ball, slowing its travel down considerably. A serve, for example, might begin with the ball moving at 150 mph. By the time it meets the opponent’s racket, the increased drag has reduced it to as little as 50 mph.

Fuzz also creates a wake of air behind the ball that increases its backspin or topspin, making it less predictable and forcing players to react depending on how their opponent has struck the ball. The material also helps tennis rackets make secure surface contact, giving the player more control and accuracy.

Fuzz therefore makes the game of tennis possible. A naked rubber ball would be traveling too fast for players to be responsive to it. It would also likely be moving too quickly for spectators to easily track the ball with their eyes. And depending on the serve, a fuzz-less ball could even double as a projectile, injuring the player attempting to return the ball. While combat tennis would probably find an audience, it's not exactly what Wimbledon is up to.

If all tennis balls have a nap, why do players bother looking at them? It comes down to how that fuzz is holding up. Brand-new balls have smooth, flat naps that will make the ball travel faster. Some players like that, especially on a serve; others may prefer a slightly older ball with fuzz that’s fluffier to retain more control over the ball.

In the 1800s, tennis balls were covered in flannel {PDF}. Today, manufacturing techniques can vary. Wilson, one of the biggest names in tennis, uses a felt covering made of two-thirds wool and one-third nylon. (Wool is better equipped to maintain its shape.) Heat cures the adhesive; a wash returns the fuzz to full thickness, which may have been dampened down during assembly. The ball is now ready for the court—and for people to argue whether it’s yellow or green.

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