The invention relates to an inflatable ball for ball games, in particular football, comprising an outer ball having interconnected parts consisting of twelve equilateral pentagons and twenty equiangular hexagons, each pentagon being enclosed by five hexagons and, at the location of the connection between a pentagon and a hexagon, the sides connected to one another being of equal length.

In a design of this ball which is generally known, the hexagons are equilateral. It has been found that, in the inflated state, the stress in the material of the hexagons is markedly greater than the stress in the material of the pentagons. If the ball is kicked, the path through which the ball travels, the speed of the ball and the so-called spin will depend on the spot where the ball is struck. The behaviour of the ball when it bounces is also dependent on whether the ball strikes the ground with a hexagon or a pentagon. It will be obvious that such uncertainty is undesirable, in particular with top sportsmen. The difference in stress and the degree of stretch in the material of the hexagons and pentagons can be explained by imagining what happens if a perfectly spherical inner ball is inflated inside the outer ball consisting of pentagons and hexagons. It appears that the hexagons come into contact with the inner ball sooner than the pentagons, while when the pentagons are touching the inner ball in only one spot, the hexagons are already touching the inner ball with a relatively large surface.

Another disadvantage of the difference in stress and the degree of stretch in the material of the hexagons and pentagons is that the seams between the hexagons themselves are subject to greater forces and consequently split and wear more quickly than the seams between the hexagons and the pentagons. In addition, the hexagons on average wear more quickly than the pentagons, and the same goes for the protective coating layer. Apart from the behaviour of the ball regarding flight, bounce and wear, the spherical shape is also improved. The conventional football is not completely spherical and during the production process a certain number of balls are rejected as they do not meet set tolerance requirements in respect of roundness, weight and position of the centre of gravity.

The object of the invention is to avoid the abovementioned disadvantages and to provide an inflatable ball as indicated in the preamble, whose hexagons and pentagons - in the inflated state of the ball - are subjected to essentially equal material stresses and degrees

of stretch and whose spherical shape is improved.

To this end, according to the invention, the ball is characterised in that each of the hexagons has three sides of relatively great length connected to a pentagon and three sides of relatively small length connected to a hexagon, and the length of the short sides is at least 0.69 times the length of the long sides.

In order to ensure that the distance from the imaginary centre of an inflated inner ball to the centre point of the hexagons is equal to the distance of the centre of the inner ball to the centre point of the pentagons, the length of the short sides of each hexagon will have to be 0.839 times the length of the long sides.

Obviously, this ratio is to be preferred, because the material stresses and the degree of stretch of the hexagons and pentagons in the inflated state of the ball are virtually equal. Incidentally, in order to achieve the effect according to the invention, the ball according to the invention does not necessarily have to comprise an inner ball, and if the ball according to the invention does have an inner ball, said inner ball will usually be glued to the outer ball consisting of pentagons and hexagons. The invention will be explained in more detail below by reference to the figures.

Figure 1 shows a perspective view - not to scale - of a part of the ball according to the invention.

Figures 2 and 3 show a view of a hexagonal part and a pentagonal part, respectively, used in the ball according to the invention.

The ball according to the invention is composed of twelve equilateral pentagonal parts 1 and twenty hexagonal parts 2, each pentagon being connected to five hexagons and each hexagon being connected to three other hexagons and three pentagons.

According to the invention, the hexagons are equiangular, but not equilateral, the ratio between the length of the relatively short cathetuses b and the length of the relatively long cathetuses a being at least 0.69 and preferably 0.839• The length of the long cathetuses a corresponds to the length of a side of a pentagon. It has been established that by choosing 0.69 a

virtually equal to the material stress and the degree of stretch in the pentagons. As long as the value of b is in the said range between a and 0.69 a, the difference in material stress and degree of stretch will be less than when a and b are equal, i.e. when the hexagons are equilateral. The most important advantages of the invention are: