Explainer
Tennis ball types explained: ITF specs, felt and altitude
The three approved ITF ball types, the high altitude ball, pressurised against pressureless, what the felt does, and how a ball degrades in play.
By CricketTaken EditorialPublished Explainer19 min read
A tournament runs on crates. They arrive weeks early, are stored at a controlled temperature, and are opened in a specific order at a specific time, because the moment a tin is unsealed a countdown begins that nobody can pause. A ball that has sat in an opened tin for two days is not the ball that was approved, and the people who run the event know it precisely.
Tennis ball types explained in the strict sense means the three categories the International Tennis Federation writes into the Rules of Tennis, plus a fourth for altitude. Type 2 is the medium ball, and it is what you have hit every time you have played. Type 1 is harder and faster and exists for slow surfaces. Type 3 is larger and slower and exists for fast ones. The high altitude ball is a separate approval for play above 1,219 metres, where thin air makes a standard ball behave badly. Almost nobody outside a laboratory has ever seen Types 1 or 3 in a tin.
What follows is the whole specification, the tests a ball has to survive before it may be sold as approved, the difference between a pressurised and a pressureless ball, what the cloth on the outside is actually doing, why the junior game uses ball type more intelligently than the professional game does, and what happens physically to a ball over the nine games it is allowed to live.
What the governing body classifies, and what it deliberately leaves open
The ball specification sits in Appendix I of the Rules of Tennis, and it is a performance specification rather than a construction one. Nowhere does it say what a ball must be made of, how thick the rubber wall should be, or how the two halves are joined. It says how the finished object must behave.
That distinction matters because it defines the space manufacturers compete in. Two approved balls from two companies can be built quite differently and both be legal, provided each passes the same tests within the same tolerances. The tolerances are wide enough that the difference between one brand and another is genuinely felt by players, which is the root of the argument later in this piece.
Four properties are specified: mass, size, rebound and deformation. A fifth requirement, durability, applies to balls intended for professional and high-level play. Colour is also fixed, to white or yellow, with the seam required to be free of stitching.
- 254Height in centimetres the ball is dropped from
- 1219Metres above sea level where the altitude ball applies
- 7Games before the first ball change
- 9Games between every change after that
Published ITF figures. The drop height and the altitude threshold are written into the ball specification; the game intervals come from the ball change rule used in professional play.
Type 1, Type 2 and Type 3: what actually separates them
Every approved ball shares a mass window of 56.0 to 59.4 grams. That is fixed across all four categories and it is not where the differences live.
The differences live in size and stiffness.
| Property | Type 1, fast | Type 2, medium | Type 3, slow | High altitude |
|---|---|---|---|---|
| Mass | 56.0 to 59.4 g | 56.0 to 59.4 g | 56.0 to 59.4 g | 56.0 to 59.4 g |
| Diameter | 6.54 to 6.86 cm | 6.54 to 6.86 cm | 7.00 to 7.30 cm | 6.54 to 6.86 cm |
| Forward deformation | 0.50 to 0.60 cm | 0.56 to 0.74 cm | 0.56 to 0.74 cm | 0.56 to 0.74 cm |
| Return deformation | 0.67 to 0.91 cm | 0.80 to 1.08 cm | 0.80 to 1.08 cm | 0.80 to 1.08 cm |
| Intended for | slow surfaces | general play | fast surfaces | play above 1,219 m |
Read the deformation rows first, because they are where Type 1 is defined. Deformation is measured by squeezing the ball between two flat plates: a small preload force is applied to seat it, then a further load of about eighty newtons is added, and the extra distance the ball compresses is recorded. A Type 1 ball is required to compress less under that load than a Type 2, which is a plain statement that it is a stiffer object. Stiffer means less energy wasted squashing the rubber, and less energy wasted squashing the rubber means a livelier ball. That is the whole design of Type 1: give a slow surface a ball that fights back.
Type 3 works from the other end and uses size rather than stiffness. Its deformation allowance is identical to a Type 2 ball, but it is roughly seven per cent larger in diameter, which raises its frontal area and therefore its air resistance. A bigger ball decelerates more in flight, arrives later, and gives the returner more time. On a fast court that is the intervention you want, and enlarging the ball achieves it without touching the bounce.
The measurement protocol is worth a sentence because it explains why approved balls are consistent. Deformation is taken as the average of one reading along each of three perpendicular axes, and no two of those individual readings may differ by more than 0.08 centimetres. A ball that is stiff in one direction and soft in another fails even if its average is perfect, which rules out the manufacturing defect that would otherwise produce unpredictable bounces.
On rebound, Type 2 and Type 3 balls share the same window, from 135 to 147 centimetres when dropped from 254 centimetres onto a rigid block. The high altitude ball sits deliberately lower, at 122 to 135 centimetres. Published summaries of the Type 1 rebound band do not agree with one another, so it is left out here rather than guessed at; the appendix itself is the document to check if you need it.
The high altitude ball and the 1,219-metre line
Air gets thinner with altitude, and a tennis ball is unusually sensitive to that because it is light for its size and covered in cloth designed to grab air. Thin air means less drag, which means the ball slows less in flight and arrives faster. It also means less of the bounce is damped out. The combined effect is a court that plays considerably quicker than its surface would suggest, and a serve that becomes very difficult to return.
The specification's answer is a ball with a lower permitted rebound. Give it less bounce at sea level and it arrives at something like normal behaviour where the air is thin. The threshold is written as 1,219 metres, which is four thousand feet, and it applies to the specific tournament rather than to a country or a region.
Two other routes to the same result are recognised. Type 3, the larger slow ball, is also recommended for high altitude play, on the reasoning that a bigger ball catches more of whatever air there is. And a pressureless ball may be used at altitude provided it has been acclimatised there for sixty days or more, which is a way of letting the ball's internal pressure settle into equilibrium with the thin air outside rather than fighting it.
That sixty-day condition tells you something useful about how seriously the physics is taken. A ball flown in from sea level the week before is not the same ball as one that has sat in the same building for two months, and the rule refuses to pretend otherwise.
Below the threshold there is no separate specification, but the effect does not switch off at 1,218 metres. Several tour venues sit at a few hundred metres of elevation and are known to play fast for exactly this reason, without any change of ball being permitted. The consequence is that altitude is quietly one of the largest uncontrolled variables in professional tennis, and it interacts with everything else. A serve that is already difficult becomes close to unplayable, which is one of the reasons what a serve speed reading actually means varies so much from venue to venue.
How a ball gets approved, and what the process costs
Approval is annual, it is applied for, and it is not free.
A manufacturer registers through the federation's portal, submits an application for a specific ball, and sends samples to the ITF Technical Centre in London for laboratory testing. For a standard ball the submission is six dozen, seventy-two balls, which is enough to run the full battery of tests and still have samples left for durability work.
Before anything is measured the balls are conditioned. They sit for twenty-four hours in a climate-controlled laboratory at twenty degrees Celsius, give or take two, at sixty per cent relative humidity, give or take five. Rubber and wool both change behaviour with temperature and moisture, and a specification that ignored conditioning would be measuring the weather rather than the ball.
The tests then run through mass, size, rebound and deformation, and for balls intended for higher levels of play, durability. The durability rig is the interesting one: it uses laboratory equipment to simulate the effects of nine games of play, and the ball has to still be within specification afterwards. That number is not a coincidence, and it is the reason the professional ball change interval is what it is.
For the 2026 approval cycle the fee is US$3,300 per ball type. Approved balls are then published on a list that runs to hundreds of entries, which is why a tournament can specify a ball by name in its regulations and everybody knows exactly what is meant.
The list is also the enforcement mechanism. There is no ball police walking the world's courts. What exists is a rule that competitive tennis must be played with a ball from the list, and a manufacturer who wants to sell into that market therefore has to submit and pay.
Pressurised and pressureless balls are different objects
Most people treat this as a quality distinction. It is not. It is a design distinction, and the two kinds of ball get their bounce from different places.
A pressurised ball is a thin-walled rubber core inflated with air at well above the surrounding atmospheric pressure, in the region of twelve pounds per square inch above ambient. The bounce comes partly from the elasticity of the rubber and mostly from that trapped gas resisting compression. It is the livelier ball, it feels crisper off the strings, and it is what every professional match is played with.
Its weakness follows directly from its design. Rubber is not a perfect gas barrier, so the internal pressure leaks out steadily through the wall from the moment the ball is manufactured. That is why balls are sold in pressurised tins, and why the tin makes a noise when it is opened: the container is holding the pressure differential at zero so the ball does not start dying on the shelf. Once opened, a pressurised ball has a useful life measured in days of play, and it loses pressure whether it is hit or not.
A pressureless ball inverts the arrangement. Its internal pressure is essentially the same as the air around it, capped in the specification at no more than seven kilopascals, about one pound per square inch. All of its bounce comes from a thicker, stiffer rubber wall. Nothing can leak out because nothing is under pressure, so the ball does not go flat in storage and can be left in a bag for a year without changing.
What it loses is feel. A pressureless ball is heavier through the strings, duller off the bounce and harder on the arm, because the energy that a pressurised ball stores in compressed gas is instead being stored in stiff rubber that the player has to deform. Over time a pressureless ball can even get livelier as its felt wears away, which is the opposite of the normal ageing curve and is disconcerting to anyone used to the other kind.
The sensible summary is that pressurised balls are for playing tennis and pressureless balls are for teaching it, for ball machines, for public courts and for anywhere the cost of replacing balls constantly is the binding constraint.
The felt is not a covering, it is the aerodynamic surface
The cloth on the outside of a tennis ball is a blend of wool, nylon and cotton, cut into two dumbbell-shaped pieces and bonded over the rubber core so that the joins form the familiar curved seam. It is not there to protect the rubber, and it is not there to be visible.
It does three jobs.
The first is drag. A smooth sphere of the ball's mass and size, launched at serve speed, would arrive considerably faster than a tennis ball does. The raised nap of the felt disrupts the airflow and increases resistance, and the sport is built around the flight times that result. Remove the felt and tennis becomes unreturnable.
The second is grip. Spin depends on the ball's surface being able to hold against the strings during contact rather than sliding across them. Felt gives the strings something to bite, and it is one half of the partnership that makes heavy topspin possible; what the strings contribute to that same interaction is the other half.
The third is bounce behaviour. When a ball lands, the felt is the first thing the court touches. It compresses, it shears, and how much friction it generates against the surface determines how much forward speed the ball loses and how steeply it comes off. A ball with fresh, dense nap grips more than a ball whose nap has been flattened.
All three of those properties change as the ball is used, and they do not all change in the same direction, which is why a used ball is not simply a slower version of a new one.
How a ball is put together, and why the seam has no stitching
The construction sequence is short and the constraints on it are unusually tight.
A rubber compound is formed into two half shells. The two halves are joined to make a hollow core, and in a pressurised ball the interior is charged with gas as part of that process, either introduced directly or generated chemically during curing. The joined core is then cured, ground to a consistent diameter and roughened so that adhesive will take. Two panels of cloth, cut in the dumbbell shape that allows two flat pieces to wrap a sphere without wrinkling, are glued over the outside. Finishing raises the nap and brings the ball to its final dimensions.
The rules require the seam to be stitchless, and the reason is aerodynamic rather than cosmetic. A stitched seam would be a raised, repeating feature at a fixed position on the surface, and a spinning ball with a raised seam behaves like a cricket ball: the airflow separates differently on either side and the ball swings. Tennis is not built for that, so the seam is a glued butt joint that sits flush and the ball's flight depends only on its spin and its nap.
Colour is the other externally visible specification, and it has a date attached. Yellow was adopted in 1972 to make the ball easier to follow on television, and it took a long time to become universal, with Wimbledon continuing to use white balls until 1986. The rules still permit white, and essentially nobody uses it.
What the felt does differently on clay, grass and hard courts
Surfaces attack the felt in different ways, and the ball's ageing curve is surface-specific.
On a hard court the abrasive acrylic sands the nap. Early in a ball's life the fibres are raised by the roughness, which increases drag and makes the ball fly slower and sit up more. Later the fibres are worn off entirely, the ball goes bald in patches, and drag falls again. Hard courts are the harshest environment for the covering and the reason balls visibly change colour within a set.
On grass the surface itself is soft and the felt survives longer, but the ball picks up moisture and grass stain, and moisture adds mass. A damp ball is heavier, flies lower and sits down more, which is part of why early-round grass tennis in the morning plays differently from the same court in the afternoon.
On clay the felt does not so much wear as fill. Loose crushed brick works into the nap, adding mass and changing the surface texture, and a ball that has been through a long baseline exchange comes back visibly orange and noticeably heavier. That is a large part of why the surface is exhausting: the player is hitting a slightly different, slightly heavier object every few points, and the effect compounds through a long match. The interaction between the dressing and the ball is one of the defining features of how a clay court actually plays.
None of these effects is in the specification, because the specification tests a ball in a laboratory rather than in a match. The gap between the two is where most of the tour's argument about balls actually sits.
The junior stage balls, and the one place ball type is used as designed
The professional game has three ball types and uses one. The junior game has a graded system and uses all of it, and it is the better piece of design.
Under the federation's staged approach, children start with a red ball, then progress to orange, then green, before moving to a standard yellow ball. The grading is by compression relative to a standard ball. The red ball is around a quarter of the compression of a yellow one and is made noticeably larger, sometimes in foam rather than felt. The orange ball is around half. The green ball is around three quarters and is standard size, which is why it looks almost identical to an adult ball and is often mistaken for one.
Each stage comes with a smaller court, a lower net and a shorter racquet, and the point of the whole arrangement is that a slower ball bounces lower and travels less far, so a small child can actually rally rather than chase.
The reason this matters to an adult reader is that it demonstrates what ball specification can do. Changing the ball changes the game more than changing almost anything else, and the junior pathway is proof of the size of the effect. Everything Types 1 and 3 were meant to achieve for adults, the staged balls achieve for children, because someone actually mandated their use rather than leaving it to tournaments to choose.
What happens to a ball across nine games
The nine-game figure is not arbitrary. It is the number the durability test simulates, and it is the number written into the ball change rule. Here is what the ball is doing across that span.
- The tin is openedThe pressure differential between the tin and the room disappears and the ball begins losing internal pressure through the rubber wall. The clock starts here, not at the first serve, which is why balls are opened on court and not in a store room.
- The warm-upFive minutes of hitting, plus serves, works the felt and takes the first energy out of the rubber. This is real wear, which is why the first set of balls is retired two games early rather than at nine.
- The first two or three gamesThe ball is at its best and also at its most changeable. The nap lifts from contact with the court, drag rises slightly, and the ball starts flying a fraction slower than it did out of the tin.
- The middle of the cycleInternal pressure has fallen measurably. The ball deforms more on impact and returns less of the energy, so it comes off both the court and the strings a little slower and sits up a little less.
- Mass creeps upwardOn clay the nap fills with dressing, on grass and in humidity it takes on moisture, and on a hard court it collects rubber and dust. A heavier ball is harder to accelerate and punishes a late swing more.
- The felt goes unevenWear is not symmetrical, because one part of the ball takes more impacts than another. An unevenly worn ball wobbles slightly in flight and behaves less predictably off the strings, which players notice long before spectators do.
- The last game before the changeThe ball is measurably softer, heavier and draggier than the one that came out of the tin. Servers feel it first, because a serve is the shot with the least margin and the longest flight.
- The changeNew balls arrive and the match speeds up for two or three games. Returners have their worst statistical patch, servers have their best, and both sides know it well enough to plan around it.
A constructed sequence describing the physical changes a pressurised ball undergoes across a professional ball cycle. The direction of each change is well established; the size of each depends on the surface, the players and the weather, and is deliberately not quantified.
The practical effect is visible in play. A break of serve is a harder proposition immediately after a ball change, and players who are behind will sometimes visibly slow the game down to reach a change with the serve in their favour. Ball condition is a tactical variable, not just an equipment one.
Why the first change comes after seven games and every nine after that
The interval looks odd until you count the warm-up.
Before a professional match the players hit for several minutes with the match balls, including serves. That is a real load, roughly comparable to a couple of games of play, and it happens before a single point has been scored. Retiring the first set of balls at seven games rather than nine simply adds the warm-up back in, so the first set has done about as much work as every set after it.
The nine-game spacing after that has a second, purely practical reason. Games alternate service, and changeovers happen at odd game totals, so a nine-game interval always lands at a changeover. Balls can be swapped while players are sitting down rather than in the middle of a game, and the ball kids have a fixed routine rather than an improvised one.
The number itself traces back to the durability test. A ball is approved on the basis that it survives a simulation of nine games and remains within its permitted ranges. Changing at nine games is therefore not a courtesy to the players, it is the interval at which the governing body is prepared to guarantee that the object on court still meets the specification it was approved against.
Why ball choice is the most contested equipment argument on tour
Here is the fact that generates the whole dispute: professional tennis does not use one ball.
Different tournaments contract with different manufacturers. Among the majors, the Australian Open is played with Dunlop, Roland Garros and the US Open with Wilson, and Wimbledon with Slazenger. Below that, tour events strike their own supply deals, and the men's tour has a partnership with one manufacturer that covers only a portion of its calendar. The result is that a player can move through three or four different balls in a month while the surface, the racquet and the strings all stay the same.
Players have complained about this for years, and the complaint has sharpened from a preference into a health argument. Leading men have publicly linked frequent changes of ball to wrist, elbow and shoulder problems, on the reasoning that the arm adapts to a specific impact and is then asked to adapt again a week later. A common description is that some balls feel heavy through the strings and require significantly more force to do anything with, which is exactly the loading pattern that produces overuse injury.
Both tours have responded by opening a review of ball supply, and the direction of travel has been toward centralising the choice of supplier rather than leaving it to individual tournaments. That is an unusually direct concession that the problem is real.
Two things are worth separating carefully. The first is that the causal claim, that ball churn causes injury, is asserted by players and has not been demonstrated by any published study that would settle it. The second is that the underlying observation is not in dispute at all: the balls genuinely are different, they are different within the tolerances the specification allows, and a specification wide enough to permit that difference was written for a world in which players did not fly between four manufacturers' products in a fortnight.
There is also a straightforward commercial reason the problem persists. Ball contracts are worth money to tournaments, and a centralised supply deal takes that money out of their hands. Equipment standardisation in any sport is usually a governance question dressed as a technical one, and this is no exception.
The environmental problem nobody has solved
Roughly 325 million tennis balls are made each year, producing in the region of 20,000 tonnes of waste, and the material does not biodegrade. A ball is a bonded assembly of vulcanised rubber, wool, nylon, cotton and adhesive, which is close to the worst possible case for recycling: separating the components costs more than the components are worth.
Reuse schemes exist and are genuinely useful at the margins. Balls go to schools, to dog charities, to walking frames and to riding arenas. None of that touches the scale of the problem, because the professional game alone gets through enormous quantities and the recreational game gets through far more.
The obvious lever is the one nobody wants to pull. Pressureless balls last for months rather than days and would cut the volume dramatically, and they play badly enough that no serious player will accept them. That trade is the entire environmental conversation about tennis balls in one line, and it has not moved in decades.
What to look for, and how to judge a ball yourself
You do not need a laboratory to read a ball's condition.
Squeeze it between finger and thumb. A fresh pressurised ball resists firmly and springs straight back. One that has been sitting in an open tin for a week gives noticeably more and returns more slowly, and that softness is the pressure that has left through the wall.
Look at the nap under a light. A new ball has a short, even, slightly raised surface. A ball that has been played on a hard court has flattened, shiny patches where it has been struck and worn ridges elsewhere, and that unevenness is what makes it fly unpredictably.
Bounce it on the court and compare it against a new one from the same tin, dropped from the same height at the same time. The difference in rebound will be obvious to the eye, and it is the same measurement the approval laboratory takes with better equipment.
When watching a match, count the games since the last change. Serving in the eighth game of a cycle is a harder proposition than serving in the second, and a player who holds comfortably on old balls has done something more impressive than the scoreline shows. The pattern is easiest to see on a fast surface, where the ball's condition and the court's are compounding, and the relationship between the two is set out in the piece on how court surfaces differ.
For the wider picture of how the sport's rules, equipment and calendar fit together, the tennis section has the rest of it, and the blog archive carries the same treatment across every other sport.
Common questions
How many types of tennis ball does the ITF recognise?
The Rules of Tennis define three types for standard play, plus a separate high altitude ball. Type 2 is the medium ball used in almost all tennis everywhere. Type 1 is harder and faster and is intended for slow surfaces, Type 3 is larger and slower and is intended for fast ones, and the high altitude ball is specified for play above 1,219 metres.
What is the difference between pressurised and pressureless tennis balls?
A pressurised ball holds air inside the rubber core at well above the surrounding air pressure, and it bounces because of that internal pressure plus the elasticity of the rubber. A pressureless ball has essentially no internal pressure and gets its bounce entirely from a thicker, stiffer rubber wall. Pressurised balls play better and die within days of opening; pressureless balls play duller and last for months.
Why are tennis balls changed after seven games and then every nine?
The first set of balls is retired two games early because the pre-match warm-up has already been hit with them, so seven games of play plus the warm-up is roughly equivalent to the nine games that follow. After that the interval is nine games so that the change always falls at a changeover, and so that no set of balls is asked to do more work than the approval testing simulates.
What is a high altitude tennis ball?
It is a ball approved specifically for play above 1,219 metres above sea level, where thin air produces less drag and a standard ball flies and bounces further than it should. Its permitted rebound band sits lower than a standard ball's, which compensates for the altitude. Pressureless balls that have been acclimatised at altitude for sixty days or more may also be used.
What is tennis ball felt made of?
The cloth covering is a blend of wool, nylon and cotton, cut into two dumbbell-shaped pieces and glued over the rubber core. It is not decoration. The nap raises drag in flight, gives the strings something to grip for spin, and it changes measurably as a ball is used, which is a large part of why a used ball behaves differently.
Why do professional players argue about tennis balls so much?
Because the tour does not use one ball. Different tournaments contract with different manufacturers, so a player can change ball type several times in a month while every other variable stays the same. Leading players have publicly linked that churn to arm injuries and asked for standardisation, and the tours have opened a review of ball supply in response.
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