Follis (ball)

Follis (a term used in Ancient Rome), or Ball of wind (pilota de vent in Catalan), a term used in the 15th and 16th centuries in Spain and Italy, was a hollow ball inflated with air under pressure, able to jump and bounce when impacting at a certain speed with any solid body. Different types of balls of wind were commonly used to play a variety of ball games that were popular in that particular period of time.

Today, although many of the existing balls are inflated with air, the modern name is simplified to "ball" regardless of the system.

History
There are studies that deal with this issue in some depth, citing numerous documents from famous authors Alfonso X of Castile who banned the "juego de pelota" with imprisonment, Desiderius Erasmus, Rabelais, Calderon de la Barca, Baltasar de Castiglione, and Antonio da Salò Scaino).

The ancient Greeks played "ball games", although it is not documented whether they used "inflated balls". It seems likely they could have used hollow balls as in the Roman Empire it is well documented that the Romans used "balls of wind", with the larger balls called "follis" and the smaller balls called "follicis", with Suetonius explicitly calling it a "ball of wind". The air chamber was made of animal bladders, preferably that of a pig.

When mentioning the Mesoamerican Ballgame (specifically Mexican) chroniclers used to compare the different consistency of the indigenous "caoutchouc filled" solid balls with the "air-filled" balls used in certain parts of the Iberian Peninsula.

One of the most important testimonies as regarding to the details, is the one by Luis Vives (1493-1540). Vives wrote a comparison between the Jeu de Paume (played with hard balls and rackets with gut stringing -although its name "jeu de paume" means "played with the palm") and the Spanish ball game (similar to the actual pilota valenciana and played with "balls of wind" struck with the palm of the hand).

In his testimony, Joan Lluís Vives explains the Jeu de Paume comparing the strings of the racquet from that game played in Paris, with animal gut used for the sixth string of a guitar. The demands of a tennis racket stringing being similar make strings of animal intestine well suited for this use as well.

Another closely related variant was known as balloon game. Visiting Livorno in 1677 Dutch traveller artist Cornelis de Bruijn wrote:

The balloon game is very popular here during the Shrovetide season. It consists of two teams, each of which tries to become the master of the ball, striking it over the other team. The area used as a field is enclosed with a rope all around, and the game is entertaining to watch.

According to a book of 1840, Barcelona had a place for playing a "joc de pilota," but it is not clear what kind of game or games were played in that place.

The arrival and discovery of rubber and synthetic polymers allowed an improvement in the performance of many games and sports balls.

Scaino Antonio and his work on the ball game
At the request of Alfonso d'Este, Antonio da Salò Scaino (priest, theologian and writer) documented the ball game. With reference balls of wind, he described in detail how the bladder and the small tube and a kind of Check valve (or retention) based packing, allowing the bellows to properly inflate the ball in a similar way of the one being used today. He also mentioned the habit of adding some wine inside the chamber so the balls could keep its characteristics (its flexibility) over the time. The system of "Check valve" employed in the balls of wind made of bladder, was described by Juan Valverde de Amusco and "Fray Luis de Granada."

Construction
The usual ball of wind was the bladder of an animal. Its outer surface was coated with leather and, once covered, the bladder was filled with air under pressure, using a dedicated type of bellows to inflate it.