football. Specification Construction Modern footballs are much more complex than past footballs. Most footballs consist of twelve regular pentagonal and twenty regular hexagonal panels positioned in a truncated icosahedron spherical geometry. Some premium-grade 32-panel balls use non-regular polygons to give a closer approximation to sphericality. The inside of the football is made up of a latex or butyl rubber bladder which enables the football to be pressurised. The ball's outside is made of leather, synthetic leather, polyurethane or PVC panels. The surface can be textured, weaved or embossed for greater control and touch. The panel pairs are either machine-stitched, hand-stitched or thermo-bonded (glued and bonded by heat) along the edge. To prevent water absorption balls may be specially coated, or the stitches bonded with glue. The size of a football is roughly in diameter for a regulation size 5 ball. Rules state that a size 5 ball must be in circumference. Averaging that to and then dividing by gives a diameter of about . Size and weight Regulation size and weight for a soccer ball is a circumference of and a weight of between . The ball is inflated to a pressure of at sea level. This is known as "Size 5". Smaller balls, sizes 1, 3 and 4 are also produced for younger players or as training tools. Types of ball There are different types of football balls depending on the match and turf including training footballs, match footballs, professional match footballs, beach footballs, street footballs, indoor footballs, turf balls, futsal footballs and mini/skills footballs. Professional/Premium Match Footballs are developed with top professional clubs to maximize players natural abilities and skills. They are FIFA-approved for use at the highest professional and international levels and designed for performance, exact specifications, great accuracy, speed and control. Air retention, water-resistance, and performance are far superior when compared to a training ball. Intended for all natural and artificial turf surfaces and all climates. These are the most expensive footballs. Matchday Footballs are high performance range of balls for all playing surfaces. The outer casing is either leather or an approved synthetic and it will typically be water-resistant as well. They are guaranteed to conform to official size, weight, and texture regulations, designed to suit all levels of play and all age groups. These balls cost more than turf or training balls, which is offset by their superior level of quality. Recreational/Practice/Training Soccer Balls