Pressureless vs pressurized tennis balls: the real difference

How the two kinds of ball work

Both kinds look the same from the outside: a hollow rubber core covered in felt. The difference is inside.

A pressurised ball is inflated. The ITF says the air inside a new one is typically 10 to 13 psi (70 to 90 kPa) above atmospheric pressure. That trapped air does much of the work when the ball bounces, which gives it a lively, springy feel. It is also why pressurised balls come in sealed, pressurised cans.

A pressureless ball has air at normal atmospheric pressure inside. The ITF explains that it gets more of its bounce from the rubber core, which is necessarily thicker. Under the ITF rules, its internal pressure can be no more than 7 kPa (1 psi) above the air outside.

Side by side

Do pressureless tennis balls go dead?

Not in the usual sense. In Cross and Lindsey's lab comparison of 26 balls, the softening caused by air loss did not happen in pressureless balls. Two of their pressureless balls actually got slightly stiffer over five months, which the authors put down to the rubber stiffening with age.

What does wear out is the felt. As it thins and goes bald, the ball flies and grips the court differently, even if its bounce off the floor is fine. So a pressureless ball reaches the end of its life slowly, through wear, rather than going flat in a few weeks.

How they feel in play

Pressurised balls feel lively when new, and they are what tournaments use. As they lose pressure, they slow down and the bounce drops.

Pressureless balls tend to feel firmer, because the thicker rubber does the work that the air does in a pressurised ball. They play more consistently over time, since there is no pressure to lose. That consistency is the main reason coaches like them for baskets and ball machines.

Which should you buy?

Pressureless balls and altitude

At altitude, the air outside is thinner, so a pressurised ball made for sea level is effectively over-pressurised and plays fast. A Wilson engineer told the WTA a regular ball at about 4,000 ft or higher bounces about three inches higher. The ITF approves a special high altitude ball for this, and also allows pressureless balls above 1,219 m (4,000 ft) as long as they have been acclimatised for 60 days or more at that altitude.

Can a pressurizer help either kind?

For pressurised balls, a pressurizer tries to stop air leaking out between sessions by holding the balls in air at higher pressure. No independent published test shows how much it helps, but the principle is sound. Our pressurizer guide covers what it can and cannot do.

For pressureless balls, there is nothing to keep in. The ITF says their air is at atmospheric pressure, so a pressurizer has no pressure to protect. Save it for your pressurised balls.

How to test either kind at the court

1. Keep one new ball of the same kind and model as your reference. Compare pressureless with pressureless, and pressurised with pressurised.
2. Find a flat, hard spot on the court, away from lines.
3. Hold both balls at the top of the net, 0.914 m (3 ft) in the centre, bottoms level with the tape.
4. Let go together, without pushing or spinning.
5. Watch the first bounce. From that height, a new Type 2 ball comes back to roughly 49 to 53 cm (19 to 21 in).
6. Repeat three times, swapping hands.
7. For a pressureless ball, also check the felt. If the bounce is fine but the felt is bald, it is time for a new one.

Are pressureless balls slower?

Not by the rulebook. A pressureless ball approved by the ITF has to meet the same Type 2 rebound range as a pressurised Type 2 ball: 135 to 147 cm (53 to 58 in) from a 254 cm (100 in) drop. So off the floor, a new pressureless ball and a new pressurised ball of the same type can bounce the same.

The difference you notice is in the feel and in how things change over time. A pressurised ball starts lively and drops off as it loses air. A pressureless ball feels firmer from the start and stays much the same for longer.

Why pressureless balls are only Type 2

The ITF approves pressureless balls under Type 2, the medium pace ball used on most hard courts. The rules list the pressureless option only for Type 2, so Type 1 (fast) and Type 3 (slow, larger) balls for clay and grass are pressurised balls. If you play mainly on clay or grass and want the ball the court is meant for, a pressurised ball of the right type is the way to go.

Where BallCheck fits

BallCheck works for both kinds. Put your phone on the court, drop the ball from net height and it listens to the bounces, comparing the ball with a new one of the same type. For pressurised balls, that shows you when pressure loss starts to bite. For pressureless balls, it confirms they are still consistent and leaves the felt check to you. Reference values assume lab conditions, so drop a new ball on your court first to calibrate. The free web version works in your browser today.