Tennis balls come in four speeds, three types of felt, and two basic means for producing bounce. If all combinations were possible, this would give us 4 x 3 x 2 = 24 distinct types of tennis ball, and that's before we consider individual brands. If you never thought buying a can of balls was that complicated, you were right. Some of these theoretical types would be completely illogical, others simply aren't manufactured, and for most of us, many of the existing options would be at most an occasional experiment.
Speed
Early in the year 2000, the International Tennis Federation (ITF) amended the rules of tennis to allow three different kinds of standard-altitiude tennis ball to be used in tournament play. Prior to this change, only medium speed balls for standard altitudes and high altitude balls for play at above 4000 feet were sanctioned. Now we also have "fast" balls, intended to quicken slow clay court play, and "slow" balls intended to slow play on the fastest courts, primarily grass. For a detailed explanation of how balls have been made faster or slower, see New Standards for Balls. Here's a brief summary of speed characteristics:
- Slow: larger diameter, same weight. Possibly good for players who need more time to get ready to hit the ball.
- Medium: by far the most common type of ball. Best for most players in most situations.
- Fast: hard to find and rarely used. Possibly a good choice for players who like the soft footing of clay, but would like to be able to end points more quickly.
- High altitude: designed to be easier to control in the thinner air above 4000 feet.
Felt
The felt covering on a ball is designed with a specific court surface in mind:
- Regular duty: designed primarily for clay and most indoor courts. This is finer felt designed not to fluff up excessively. It wears away quickly on the more abrasive hard courts.
- Extra duty: designed primarily for hard courts. This is denser felt that can take heavy abrasion. On clay, it tends to collect little bits of the court. On clay or slower indoor courts, it gets too fluffy.
- Grass court felt: basically regular duty felt, but treated to resist staining.
