The soccer ball’s characteristics are defined by the Act 2 of the International Football Board. The ball must be spherical, in leather or any other suitable material, having a circumference of 70 cm and more than 68 cm (that is, a diameter of 22 cm), a mass of 450 g and 410 g least at the beginning of the match and a negative pressure of between 0.6 (for futsal balls) and 1.1 atmosphere (600 – 1100 g / cm ²). Balloons of smaller sizes are used for youth tournaments, size No. 5 from 13 years , size 4 for 11 and 9 years and size 3 for beginners, 6 and 7 years .
The ideal shape is spherical and theoretical. But molding trials as for the ball of basketball were not doing something quite flexible. Technicians have therefore chosen the assembly pieces of leather. Initially, some balloons included 18 panels of leather stitched and assembled. They were closed by a lace, which, once loosened, assembled the remaining signs and contained inflation system (a hose connected to the bladder, withdrawn into itself).
Eigil Nielsen, founder of the Danish brand Select first introduced the principle of a valve in the balloon, in 1947: he wanted to replace the lace that shut the ball. And stitch to close remaining signs, so he decided to use a long curved needle to finish the seam inside the ball. This new principle was gradually causing the disappearance of laces in the balls.
Nielsen is still inventing the first balloon to 32 panels of cotton to make the ball more circular. Geometrically, the ball 32 panels can be described as a truncated icosahedron is a semi-regular polyhedron with 60 vertices and 32 faces, 20 hexagonal and 12 pentagonal, whose edges are of equal length. The outer shell is then made of 32 pieces of leather (natural or synthetic), sewn together, containing an inflatable rubber bladder. The bladder may be natural latex or butyl, a synthetic latex.
Since then, the leather has completely disappeared from the soccer ball and was replaced by foam, PVC, and polyurethane, whose quality and thickness ensures the strength, flexibility and rebound of the ball.