The Making of a Tennis Ball is a short series on what actually goes into the object every point depends on. Chapter one starts where the ball itself starts: the core.
Before it bounces, before it’s covered in felt, before it’s even round in any final sense, a tennis ball is two shells of raw rubber, pressed together around a pocket of air. Everything the ball will later do — the way it springs off a string bed, the way it compresses against a racket face at the moment of contact — starts here, in a component almost nobody watching the game ever thinks about.
An Old Problem
Tennis balls weren’t always built this way. The earliest ones were hand-wound from cloth or stuffed with hair, later with rubber solids that had no air chamber at all. They bounced, but inconsistently — every ball behaved a little differently, and players simply adjusted. It wasn’t until rubber technology matured, and manufacturers found a reliable way to seal air inside a rubber shell, that the modern hollow-core ball became possible.
That shift changed the sport more than most people realise. A pressurised hollow core meant a ball could bounce predictably, match after match, court after court. Consistency became something players could rely on — and eventually something governing bodies could regulate.
What’s Actually Inside
Strip away the felt and what’s left is two hemispheres of natural rubber compound, moulded separately and then fused together under heat and pressure, sealing a pocket of pressurised gas inside. Natural rubber is used rather than synthetic because of how it recovers its shape — after thousands of compressions against a racket, it needs to keep returning to true, match after match, without going soft or brittle.
The internal pressure is what gives a new ball its lively, fast bounce — and why a ball, once opened from its can, begins a slow, one-way process of losing that pressure over time. It’s also why the ITF sets a defined bounce-height range for a ball to be considered regulation: not an arbitrary number, but a direct measure of what that rubber shell and its internal pressure are doing.
Next in the series: The Felt.
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