How to tell a new tennis ball from a dead one

Tell a new ball from a dead one by the bounce. Play each differently.

Key facts

1
A tennis ball has three parts: a rubber core, pressurised air inside it, and a wool-nylon felt skin of roughly 60/40, about 1.5 to 2.5 mm thick.
2
A tennis ball's felt fuzz acts as an aerodynamic surface: its fibres trip the boundary layer from laminar to turbulent, which shapes drag.
Mehta, review of tennis ball aerodynamics
3
On tour, new balls usually come in after the first 7 games of a match, then every 9 games after that, though the exact ITF wording is still to be checked.
4
A tennis ball on its own is a poor spring, losing about half its energy to deformation, which is why the strings store most of the rebound.
5
The ITF drop test is reported to expect a ball dropped from 254 cm to rebound between 134.6 and 147.3 cm, a figure still to be checked against the current rules.
ITF Rules of Tennis, ball approval

Why it works

The core and the air pressure inside it set the bounce. The felt sets the flight. The fuzz is an aerodynamic surface that trips the air flowing around the ball and changes its drag. Two parts doing two jobs means two separate lifetimes.

Early wear raises the nap. Drag goes up, and the ball flies slower and shorter. That's why a slightly used ball can play slower than one straight from the can. Later the pressure leaks and the felt mats down, and the ball bounces lower and deader.

The two deaths are out of phase: flight changes first, bounce later. The tour changes balls before the second death arrives. Clay and grass wear the felt faster, because surface grit abrades it.

The line to say on court
“Fluff first, then flat. Two deaths, and the balls change before the second.”

Drill: The nine-ball sort

10 min · with a partner

Have your partner mix three new balls, three balls from one session and three dead ones.
Watch your partner drop each ball from shoulder height and call it from the bounce: new, used or dead. Your partner keeps score.
Rally five balls of each type and note where your usual rally ball lands relative to the baseline.

Number to beat8 of 9 balls called right from the bounce

More drills like this: point play

Faults and fixes

Practising with dead balls, then playing with new ones

Your depth is calibrated to a low bounce.

FixOpen a can for the last 20 minutes of practice.

Trusting new balls to go long

The fluff phase can shorten flight first.

FixWatch two returns before you move your target.

Ignoring the ball change in a match

The bounce changes under you.

FixTrack the game count and adjust your targets at the change.

Questions players ask

Why do new tennis balls play differently from old ones?

The felt and the internal pressure wear out on different schedules. Fluffed felt adds drag and shortens flight, and lost pressure lowers the bounce.

Do new balls help the server?

Players often say play quickens after a ball change, but that's a claim to test against data, not a settled fact. What's certain is that flight and bounce differ from the balls you just played.

How often are balls changed in pro tennis?

The usual tour rhythm is new balls after the first 7 games, then every 9 games. Check the exact wording in the current ITF rules.

Why do balls wear out faster on clay and grass?

Surface grit on clay and grass abrades the felt, so it ages faster than on smoother courts.

What this doesn't cover

There's no licensed test data yet on exactly how fast a ball fluffs and loses pressure, so the two-stage wear curve is a shape, not a measurement. Whether new balls give the server a real edge is still a question for data. The ITF ball-change wording and drop-test figures should be checked against the current rules.

Sources

Mehta, review of tennis ball aerodynamics
ITF Rules of Tennis and ball approval

StrikeHow to test if your tennis balls are deadTo test a tennis ball, drop it from 254 cm and measure the rebound: by ITF rule it must come back up between 134.6 and 147.3 cm. Below that, it's outside the rule. A dead ball bounces lower and flies shorter, so practising with one grooves a swing for a ball you won't meet in a match.Play the pointHow clay, grass and hard courts change your gameClay, grass and hard courts play differently because of two things at the bounce: friction, which takes forward speed, and restitution, which sets bounce height. Clay grips the ball and kicks it up, so points run longer. Grass is slick, so the ball skids low and rewards the serve and first strike. Hard courts sit between, tuned by the sand in the coating.Play the pointHow to play tennis in wind, sun, heat and altitudeTo play tennis in the wind, check it before the warm-up and change your margins. Into a headwind, give the ball more net clearance and a full swing, because the wind holds it in. With a tailwind, take pace off and aim shorter. Lobs and kick serves hang longest, so the wind moves them most.StrikeHow string tension and type affect spin in tennisSpin comes mostly from string snapback, not tension. During contact the main strings slide sideways and snap back as the ball leaves, adding rotation. Slick polyester slides further than nylon and, in one test, gave roughly 20% more spin. Tension barely changes ball speed, so a steeper swing path is the bigger fix. Strings also lose tension from the first minute.