A tennis ball is constructed in two rubber halves, which are glued together during the production process. Afterwards, the felt is placed on the tennis ball in two parts and the seams are filled up with liquid rubber. A tennis ball must comply with a number of mandatory technical specifications (eg. a diameter of minimum 6.35 and maximum 6.67 millimetres and a weight of minimum 56.7 and maximum 58.5 grams). The quality of a tennis ball depends on - among other things - the quality of the rubber, the felt layer and the glue used. The colour of the felt is important, since the visibility of the tennis ball is determined by it. The bright yellow colour doesn't only ensure that the tennis player sees the tennis ball quicker and clearer, it also ensures that the public can follow the tennis ball and the tennis game more easily. Most tennis balls are suited for all courts and surfaces. Similar to tennis rackets and tennis strings, the choice of tennis balls is a personal one. Playing regularly or too long with too soft or too heavy (moist) tennis balls, can lead to a forced or unnatural stroke and as a result arm injuries can occur.
Gas filled or pressurised tennis balls
- pressure in the core of the tennis ball is greater than the pressure outside of the tennis ball (so there is an inside pressure)
- just before glueing together the two rubber main halves, a small pellet of solid material is added. During the remainder of the process, that small pellet transforms into a gas which generates pressures inside the tennis ball
- because the rubber inside a tennis ball is never 100% air tight, the gas slowly evaporates from the tennis ball. To avoid new tennis balls losing pressure while they are still wrapped up, the can is also put under pressure. That's where the name gas filled tennis balls or pressurised tennis balls comes from
- as soon as the tennis balls are removed from the pressurised can, they start evaporating slowly, which means that after while the tennis balls start softening
- because the tennis balls slowly start losing gas after opening the can, the playing comfort slowly diminishes as well. That is one reason why professional players change tennis balls every nine games .
- gas filled tennis balls play very comfortably (especially in the beginning)
- pressurised tennis balls are suited for the competition tennis player and the better tennis players
- especially for tennis coaches who teach the better tennis players, there are gas filled tennis balls available at reduced prices in boxes of (by example) 24 cans.
Further classification of gas filled tennis balls for coaches per 24 cans with 4 tennis balls per can:
Pressureless balls:
- pressure in the core of the tennis ball equals pressure outside of the tennis ball (so there is no inside pressure)
- the tennis ball bounces higher because of the slightly harder rubber composition of the core
- even with a hole in the pressureless tennis ball, you can keep playing tennis
- the tennis balls will not get softer after opening the packaging, so these tennis balls do not come in a pressurised can
- pressureless tennis balls have a longer lifespan than gas filled tennis balls
- because of the harder core, this tennis ball plays less comfortable
- after a while the felt layer will wear down and the core will become harder, which will result in the tennis ball becoming quicker. This is the sign to replace the pressureless tennis ball
- a pressureless tennis ball is advised for the beginner and less demanding (regarding playing comfort) tennis player
- pressureless tennis balls with a very low bounce have been especially developed for young and beginning tennis players: the Stage 1 and Stage 2 practice tennis balls
- most of the practice balls are available in two or more colours.
Further classification of pressureless tennis balls: