Tennis balls used to be filled with dirt from the earth, with sawdust or with sand or chalk materials. By 1480 CE however, the French King Louis XI banned the act of filling tennis balls with any kind of material other than the best wool. The King also insisted that the tennis ball be crafted of high quality leather. Meanwhile, in Scotland, tennis balls were made by using a goat or sheep stomach and wrapping it with wool; the material would then be tied off with a piece of rope. In addition, some old tennis balls have been retrieved from the Westminster Hall in England when they were discovered as the site was being renovated. The latter tennis balls were made with human hair and putty stuffing and were dated back to the time when King Henry VIII ruled England. Still other early tennis balls were made with animal muscles, intestines, rope, and pine wood: these balls dated back to the sixteenth century.
By the eighteenth century, some tennis balls were being made that consisted of a rolled strips shaped into a ball like construction that was further wrapped in wool strips of material. String was then used to tie the ball up and the ball had a white covering sewn over the top of it. By the 1870s, vulcanized rubber was created and this material was used to make improved tennis balls; these balls were offered in sleeves of four to a package when they were sold. Today only white or yellow balls are used in the US for professional games and the most common tennis balls on the court are those in optic yellow. This color is more common because studies conducted in the early 1970s revealed that it makes the ball easier to see while viewing televised tennis events.
Present day tennis balls are made to meet specific gaming regulations; tennis balls are 2.63 inches or 6.7 centimeters in diameter. The balls are made with a bright yellow exterior so that they can be easily viewed when in motion, however, there are recreational tennis balls offered in a variety of unique colors. The exterior of the modern tennis ball is coated with a felt-like, fibrous material: this material tends to make tennis balls more aerodynamic. Tennis balls are also hallow and light weight; this too lends to their aerodynamic properties.