What are the best tennis balls for each surface?

Are tennis balls as important as court speed?

Tennis aficionados know that court speed is a variable often discussed by pundits at the start of an event.  For instance, we hear comments like ‘there has been more grit added to the court surface’ at the US Open, slowing it down and making the ball bounce higher. We are also often shown charts of how the court speeds of the Masters Series 1000 events compare and have trended over time:

What fans don’t often hear is a detailed description of the balls used at a given event (which often differ between the WTA and ATP matches) and the consequences for play. How much do the ball specifications actually matter? Are they deserving of more airtime than they currently receive?

The short answer is yes - tennis balls very much matter.  For example, in 2011, the French Open switched to Babolat from Dunlop and players claimed that the balls bounced higher and played faster. That was the last time Roger Federer made the final in Paris, and Paul Annacone - his coach at the time - said, “The baseliners were complaining because it was a very quick ball.” Players also criticize the balls they have to play with from time to time as Nadal did in Shanghai when he found the quality to be sub-par. Andy Murray was irate when he found a ball used for the WTA matches in the mix during his match at the Miami Open a couple of years ago.

After doing some research, it was clear that even though we are passionate tennis fans who played at a high level (and can discern the difference in feel between Babolat and Slazenger balls, for instance) there was a lot we didn’t know about a major element of the game. This article aims to illuminate the most interesting aspects of tennis balls: their evolution, specifications and implications for how the game is played.

How are tennis balls manufactured?

As you might have read from a previous post on our blog, Lawn Tennis (or the modern game as we know it) has evolved from Real Tennis in the 1870s. One of the main distinctions between the two games remains the properties of the balls: Real Tennis balls have been traditionally made from a spherical stitched envelope of leather or cloth stuffed with rags, horsehair or similar material, while tennis balls have a rubber core.

The vulcanisation (hardening of rubber) is a manufacturing process created by Charles Goodyear in the 1850s and applied to tennis balls. In this era, tennis balls were made solely of rubber, but the wearing and playing properties of the balls were improved by covering them with flannel stitched around the rubber 'core'. The next innovation involved making the core hollow and pressurising it with gas.

At that time, the core manufacture was based on the 'clover-leaf' principle whereby an uncured rubber sheet was stamped into a shape resembling a three-leaf clover and this was assembled into a roughly spherical space by machinery adapted for the purpose. Chemicals generating pressurising gas were added prior to sealing the rubber and these were activated when moulding the core to a spherical shape in heated cavities.

The process was used for many years until the precision of the game demanded a higher degree of uniformity (particularly relating to wall thickness) than could be obtained with the clover-leaf method. Now the manufacturing process encomapasses moulding two separate 'half-shells' which are assembled together to produce a 'core'. The original flannel cloth was replaced by special 'melton' cloth made specifically for the Lawn Tennis and the stitching has been replaced by a vulcanised rubber seam.

If you want to learn more about this process, Wilson provides a fascinating visual overview.

How have tennis balls evolved (or not) over the years? 

In brief, the evolution has been minor and shifts in specifications have been rare. A 1925 rule decreed that tennis balls must bounce 53 to 58 inches when dropped from 100 inches. That regulation has not changed.

The biggest visual change came in 1972 when most tournaments switched to yellow balls from white ones because they stood out more on television. Nevertheless, Wimbledon stuck with white balls until 1986 (black balls were also produced en masse in the early years of Lawn Tennis).

In the 1980s, metal cans gave way to plastic (although the trend has recently been reversing), and high-altitude balls, which bounce less, made their debut.

Today one of the remaining quirks is that some regions supply cans with 4 balls (i.e. the UK) whereas others just provide 3 balls (i.e. North America).

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What are the specifications of tennis balls used in professional events? 

The ITF maintains an extensive list of ‘approved balls’ on which ~200 brands are represented (!). For any location and court type there is a variety of balls available to the player, in addition to the standard (Type 2) ball. A slightly harder, fast-speed ball (Type 1) which is intended for use on ‘slower’ court surfaces, and a larger, slow-speed ball (Type 3) for faster courts.  

The rules require ball diameters to hover between 2.57 and 2.70 inches but each manufacturer can choose their own felt makeup and weaves (often a nylon-wool blend). In addition, a ball’s mass can range from 56 grams to 59.4 grams, which is a considerable variation.

There are two main classifications which mainly pertain to the felt cover: extra duty or regular duty. ‘Extra duty’ is designed for heavy wear and tear on hard courts while ‘regular duty’ has stain resistant features which are more important on clay and grass than sheer durability.

What does the weight difference mean in practical terms? A heavier ball stays down more when sliced and lower air pressure requires more pop from the player to produce pace. Some players change their string tension based on which balls a tournament uses but daily environmental factors also matter: for example, heat makes rubber bouncier, but humidity makes the balls heavier.

Which tennis balls are used in major tournaments?

Tournament officials decide which ball their event will use, usually depending on sponsorship deals. The Australian Open made a deal with Dunlop in 2018 (the tournament previously had a long-standing partnership with Wilson), Wilson balls are used in the US Open, Babolat supplies the French Open, Slazenger partners with Wimbledon, Dunlop balls are used on Europe’s clay-court Masters 1000 tournaments and Penn balls are used for the North American hardcourt tournaments on the ATP Tour.

Each ball variant is made bespoke for specific surfaces. For example, lighter felt can wear quickly on abrasive hard courts and drastically speed up the game, so the ATP Tour elects to use a more durable felt option than the WTA. However, the felt material chosen for hard courts is less suitable on soft surfaces like clay because instead of wearing off, it fluffs up too much and picks up debris which impacts the feel and behaviour of the ball. Hard court balls typically opt for a heavy-duty felt in a looser weave for durability, while the softer surfaces move toward a tighter weave, which fluffs quicker.

When producing roughly 100,000 balls for the US Open, Wilson’s factory earmarks several presses just for the balls to be used at the event in order to minimize variation. One in every 400-500 balls is defective, so an umpire makes cursory checks on each ball when they are opened on the court before the match.

Slazenger - provider of Wimbledon balls since 1902 - is known for being a heavy ball and includes a water-repellent barrier dubbed ‘Hydroguard’ to protect it from rain and moisture in the air. The heavy ball bounces low on a surface which already produces low bounces and slows down the play to a degree because it takes more pop to get pace behind it. A little known fact: balls at the AELTC get opened each morning and then placed in a refrigerator courtside at 68 degrees Fahrenheit to attain what is deemed to be the ‘ideal condition’.

Babolat, which took over from Dunlop at Roland Garros in 2011, provides balls with felt that would be disastrous on a hard court but allows for a desirable high-rebound off the clay. The French Open ball hasn’t changed in four years so I think Rafa has been pretty satisfied with the quality produced by the French company…  

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