Can you make tennis balls bouncy again?

First, why did the ball go flat?

There are two different problems, and only one can be fixed.

The first is pressure loss. A new pressurised ball holds air at about 10 to 13 psi (70 to 90 kPa) above the air outside, according to the ITF. After the can is opened, that air slowly leaks out through the rubber, and the ball bounces lower. Air can also go the other way, which is why this part is reversible.

The second is wear. Every hit flattens the ball, fluffs and strips the felt, and fatigues the rubber. A ball with bald felt or a cracked core will not play like new whatever the pressure inside it. If your ball is worn, the honest answer is to move it to the practice basket.

What works: storing balls under pressure

University of Illinois physicists answer this question directly: people do re-pressurise tennis balls at room temperature just by storing them in a few atmospheres of pressure. If the air around the ball is at higher pressure than the air inside, air slowly works its way back in through the rubber.

That is the idea behind pressurizers. Makers quote very different pressures. Tourna says its Restore tube compresses air with 14 psi. Pascal Box says regeneration needs at least 29 psi around the ball and that its box holds 48 psi. These are figures from the companies selling the products.

How well it works in real life is not proven. We found no independent published test with numbers. A 2025 UCLouvain master's thesis that modelled pressure retention tubes concluded they can significantly slow pressure loss or even reverse it, but its full text is not public until 2027. Our guide on whether pressurizers work goes deeper.

What sort of works: warming the ball

Heat makes rubber livelier. The ITF says high temperatures increase bounce height, which is why its tests run at a fixed 20 °C (68 °F). So a ball warmed in your hand, a pocket or the sun will bounce higher for a while.

That is not a repair. The boost fades as the ball cools, and nothing has gone back inside it. The Illinois physicists add that warmth makes it easier for air to move through the rubber, which could speed up re-pressurising in a pressurizer, but finding a temperature that helps without damaging the ball would take experimenting. We would not try it.

What doesn't work

• Needles and valves. Injecting air or gas leaves a hole, as the Illinois physicists point out, and the air will leave through it.
• Autoclaves, ovens and boiling water. The polymers in a ball are unlikely to survive that kind of heat without damage.
• Washing or brushing the felt. It can tidy up the look, but it does not add pressure, and wet felt makes a ball heavier until it dries.
• Home made pressure containers. Bottles and jars not built for pressure can fail suddenly. If you want to try re-pressurising, use a product made for it.
• Anything on a pressureless ball. The ITF says pressureless balls are at normal air pressure and get their bounce from a thicker core, so there is no pressure to restore.

Methods compared

How to check whether your fix worked

You need a before and after test on the same floor, at the same temperature, compared with a new ball. Otherwise you are only guessing.

1. Number your flat balls with a marker so you can track each one.
2. On a hard, flat floor at room temperature, drop each one side by side with a new ball from net height, 91.4 cm (3 ft). Note how far below the new ball it bounces.
3. Put the flat balls in the pressurizer for the time the maker recommends. Keep one flat ball out as a control.
4. After that time, let the balls sit at room temperature for an hour, so warmth from handling is not giving you a false boost.
5. Repeat the side by side drop with the same new ball, on the same spot.
6. If the pressurised balls now bounce closer to the new ball than the control does, the pressurizer is helping. If not, retire them from matches.

What to do with old tennis balls

• Practice baskets and ball machines, where a slightly lower bounce matters less than having lots of balls.
• Drills for kids, or slow rallies for beginners.
• Club ball collections. Some clubs and federations run recycling or reuse schemes, so ask before you throw balls away.
• Around the house: chair and walker feet, massage balls, or a padded marker in the garage.

How long does a revived ball stay bouncy?

Not for long once it leaves the pressurizer. Taking a ball out puts it back at normal air pressure, and air starts leaking out through the rubber again, just like a freshly opened ball. Play speeds this up. So a pressurizer is best thought of as storage between sessions, not a one off repair.

That is also why the test above waits until the balls have come out and settled. If you test straight from the tube, you are testing the best moment of the cycle. Testing again after a session shows you how quickly the gain fades for the way you play.

Why a used ball can feel livelier than a new one

Before you try to fix a ball, make sure it needs fixing. In Cross and Lindsey's study of 26 balls from 8 brands, most balls bounced slightly higher after a simulated wear test, some by more than 1.5%, even though they got softer. An older lab thesis found machine-fatigued balls bounced higher than new until about 3,200 impacts. So a ball that feels soft in your hand can still bounce in range. Drop it next to a new ball before you write it off.

Know if it is worth saving

BallCheck makes the before and after test quick. Put your phone on the floor, drop the ball from net height and it compares the bounce with a new ball of the same type, giving a score out of 100 and a call: keep, pressurize or retire. Premium keeps a history per ball, so you can see whether a pressurizer is moving the score. Reference values assume lab conditions, so calibrate with a new ball on your own court first. The free web version runs in your browser today.