Tennis ball pressure, felt, and how long a can really lasts

Tennis ball pressure is what makes a new ball live. Inside a pressurized ball, the air sits roughly 12 to 14 psi above the atmosphere outside it — close to double the surrounding pressure. That gas escapes through the rubber within weeks, whether you play with the ball or not.

How tennis ball pressure works

A tennis ball is a hollow rubber shell a few millimeters thick, wrapped in two dumbbell-shaped panels of felt. On its own that shell is soft. Trapped gas pushing outward stiffens it, so when the ball meets the strings or the court it flattens for a fraction of a second and snaps back instead of staying squashed. Less time deformed means less energy lost as heat and more of it returned as bounce. That is the whole reason tennis balls are pressurized.

Cores hold air or nitrogen, the latter on the reasoning that it works through rubber more slowly. Rubber is permeable either way, so the ball is on a clock from the day it's made.

What the ITF bounce test measures

The ITF regulates how a ball behaves, not what's inside it, and the headline test is a drop test. A standard Type 2 (medium) ball dropped from 100 inches (254 cm) onto a concrete base must rebound between 53 and 58 inches (135–147 cm). It also has to weigh 56.0 to 59.4 g, measure 2.57 to 2.70 inches across (6.54–6.86 cm), and flatten roughly 0.22 to 0.29 inches under an 18 lb compression load.

Other categories cover other conditions. Type 1 (fast) balls are firmer, for slow surfaces like clay. Type 3 (slow) balls are at least 6% wider, which adds drag. High-altitude balls rebound lower by spec, near 48 to 53 inches from the same drop, since thin air already gives the ball extra flight. Testing happens around 68°F (20°C), and a cold ball bounces lower until it warms.

Why a fresh can hisses, and why balls still die

The can is pressurized to roughly the same level as the balls inside it. With no pressure difference across the rubber, the gas has nowhere to go, so the balls hold their bounce on the shelf for years. The hiss when you pull the tab is that seal breaking.

From there they leak. An opened can goes soft in about two weeks even if nobody hits with it. Unopened cans aren't immortal either — they lose pressure through the lid and seams, so one that sat in the garage for years can open with a weak sigh and three dead balls.

How long do tennis balls last

Two things fail, on different clocks.

Pressure goes first for most players. Opened balls hold full bounce for about a week of regular play, feel soft by two weeks, and are dead within a month. You feel it before you see it: the ball sits up shorter and heavy topspin stops kicking off the court.

Felt goes fast on abrasive surfaces. Two hours on a gritty outdoor hard court can shave the nap smooth while there's still pressure left, and a slick ball starts flying long. On clay the opposite happens: the nap picks up court material, fluffs, and the ball plays heavy. To judge a suspect can, drop one beside a new ball from the same height; a visibly lower rebound means it's drill-feed material now.

Regular duty vs extra duty tennis balls

The difference is the felt, not the pressure. Extra duty balls carry thicker, looser-woven felt built to survive abrasion. Regular duty balls use a thinner, tighter nap that doesn't pick up court material. Either one on the wrong surface fails early, so the court surface decides the can you buy, not your level.

Ball	Felt	Use on	Fails when
Regular duty	Thinner, tighter weave	Clay, indoor hard, carpet	Played on abrasive hard courts — wears through in a session or two
Extra duty	Thicker, looser weave	Outdoor hard courts	Played on clay — picks up material, fluffs, turns heavy
High altitude	Either weave, lower internal pressure	Above roughly 4,000 ft (1,219 m)	Played near sea level — bounces low, feels dead

What tennis ball felt is actually doing

Tennis ball felt is a wool-and-nylon blend, woven and glued on in two panels, and its job is drag. Fresh nap slows the ball through the air, grips the strings, and lets a swing put real spin on it. A worn, slick ball flies flatter and takes less spin, which is why a bald ball feels like it's rushing you. A fluffed ball does the reverse, which is why players sort through the balls in play hunting a fluffier one for a second serve.

Pressureless tennis balls and where they belong

Pressureless tennis balls invert the design. The rubber wall is thicker and stiffer, and the bounce comes from the material rather than trapped gas, so there's nothing to leak — a basket left for a year still bounces.

The trade-off is feel. They come off the strings heavier and duller, and they age in reverse: as the felt wears they get faster and slicker rather than softer. That suits ball machines, teaching baskets, and backboard work, where consistency over hundreds of hits beats tour-accurate feel. Some pressureless models are ITF approved, but the tour plays with pressurized balls.

The ball-change rule and Wimbledon's 55,000

Professional matches change balls on a game count rather than a clock: new balls after the first seven games, then every nine. The first change comes two games early because the pre-match warm-up is played with that first set, so those balls reach the first point already worn.

The count follows games, not sets, so changes usually land mid-set. The tiebreak is the common wrinkle — if a change falls due at the start of one, it's held until the second game of the next set so the balls arrive at a changeover. If the underlying counting is fuzzy, how games and sets add up covers it.

Club players can run the same rhythm without ball kids. Tennis Scoreboard is a tennis scoreboard app for iPhone and Apple Watch that tracks match scores, so the game count that tells you a change is due is already on your wrist.

That rhythm is where the famous Wimbledon figure comes from: the Championships get through roughly 55,000 balls over the fortnight, with qualifying, doubles, juniors, wheelchair events, and practice courts all drawing from one supply.

FAQ

How much pressure is inside a tennis ball?

Roughly 12 to 14 psi more than the air around it, which at sea level puts close to twice atmospheric pressure inside the shell. Makers rarely publish a figure per model — the ITF specifies bounce, weight, size, and deformation rather than pressure.

How long do tennis balls last after the can is opened?

About a week of regular play at full bounce, and dead within a month. Unopened cans keep for years but leak slowly too. Pressurized storage tubes slow the leak on balls you've opened; nothing restores worn felt.

Do pressureless tennis balls ever go dead?

Not the same way. With no internal pressure to lose, the bounce holds for years, and felt ends them instead — once the nap wears smooth they play fast and slick and stop taking spin.

How many tennis balls are used at Wimbledon?

Roughly 55,000 across the two weeks, counting qualifying, practice, and every draw. The seven-then-nine change rule is what pushes the total that high.