Sports Tech: Soccer ball design

With the 2015/16 football season well under way, a new ‘official’ ball has been introduced to Europe’s major football leagues, including the English Premiership. The Nike Ordem 3 will be seen sailing through the air and into the back of the net at grounds throughout England offering, according to Nike, the advantages of ‘accurate flight, consistent touch and maximum visibility’.

Interestingly, this very 21st-century football is not as far removed as you might think from the brick-hard leather lumps of the game’s early days. Indeed, the ball’s dry weight of 14-16oz (420-445g) was decreed as long ago as 1937, whilst the circumference was set by the Football Association way back in 1872 at 27–28 inches (now a tighter 68.5–69.5cm for pro balls).

Up to a point, the basic construction of a soccer ball has also remained the same for many decades, consisting essentially of the cover, the stitching, the lining and the bladder.

The cover is made of synthetic leather (in the past, it was full-grain leather, which tends to absorb water and wears more quickly) and is in the form of panels, which may vary from six to 32. To this is added a glossy thermoplastic polyurethane (TPU) coating to prevent water absorption and wear and tear.

Cheaper balls will be made from PVC, which is harder wearing, but does not offer the responsive feel and control of synthetic leather.

The traditional format 32-panel ball is essentially a ‘buckyball’, or truncated icosahedron, consisting of 20 hexagonal and 12 pentagonal surfaces which are stitched, glued or thermally moulded together to form a sphere.

At the other end of the scale is a ball such as Adidas Brazuca, used in the 2014 World Cup in Brazil, which has six symmetrical, interlocking propeller-shaped panels which, ironically, are intended to emulate the way air would move around a traditional 32-panel ball.

The idea behind fewer panels is that it results in a ball which is more aerodynamic, faster in flight and, as we shall see, is easier to ‘bend’.

Better-quality balls tend to be hand-stitched with five-ply polyester cord or possibly Kevlar reinforced polyester; this creates strong seams which improve durability and get a more ‘explosive’ performance from the ball.

Cheaper balls will be machine stitched or have the panels glued onto the lining, which results in a harder feel and poorer wear, whilst thermally bonded panels are becoming increasingly common on higher-end balls, although it doesn’t always have the desired effect; the thermal bonding used on the Adidas ‘Jabulani’ in the 2010 World Cup was roundly condemned by players for its unpredictable flight; particularly (and unsurprisingly), it was goalkeepers who disliked it the most. However, in general, the extremely tight seams that result from the thermal bonding process create a ball which is almost perfectly spherical, absorbs less water and has a more predictable flight pattern.

The lining – the area between the bladder and the outer cover – helps to protect the bladder, maintain the overall integrity of the ball and has a direct effect on feel and control. On higher quality balls, it will consist of four layers of polyester and cotton, whilst some balls may also have an extra layer of foam for better cushioning.
The bladder will invariably be constructed from either butyl or natural latex. Butyl retains air longer and is easier to maintain but is not as responsive as latex, which tends to be used on better quality balls for its softer touch and feel, better bounce and response.

Inflation is via valves, with higher-end balls using a silicone-treated valve that allows for smooth insertion of the inflating needle and added protection from air loss.
Claire Parnell, communications director for Nike Football Western Europe, describes how the balls go through a rigorous testing process both in the labs and on pitches “with the best teams and players around the world”. Examinations include aerodynamic tests, water absorption, kicking machine and visual acuity measures.

“We undertake in-stadium testing where players will complete a full training session and a match with the ball under lights to ensure its viability in all conditions. Then we take the ball to multiple clubs across multiple professional leagues for feedback from players and coaches alike”.

Nike’s new Ordem 3 features ‘Aerowtrac’ grooves – small surface indentations that are designed “to provide an accurate and stable flight by helping ensure a steady flow of air across the ball no matter what speed it is moving at.”

Dr Matt Carré, reader in mechanical engineering at the University of Sheffield and an expert in soccer ball aerodynamics, explains how such grooves ensure the steady flow of air across the ball.

“The main three effects on the flight of a soccer ball are drag, swerve due to spin, and erratic flight. Drag is the force that slows the ball down, in the form of pressure drag and skin friction drag. For big, bluff bodies like balls, pressure drag is the main factor. Simply put, the bigger the wake behind the ball, the bigger the drag effect will be.

“Careful design of surface roughness (seams, grooves, dimples or pimples) can reduce this level of drag by making the wake smaller, but this changes with ball speed due the behaviour of the ‘boundary layer’, a very thin layer of air near to the surface of the ball. I suspect these grooves have been designed to keep the wake small over a large range of speeds, meaning that the drag doesn’t change too suddenly.”

More high profile as far as soccer balls are concerned is spin. Carré says: “This is most famously utilised by David Beckham to ‘bend’ the ball in flight and is used for free kicks, corners and crosses. Here the player wants the ball to swerve in a repeatable, consistent way, so that the landing position can be predicted accurately.

Changing roughness will also change this. Generally, the more roughness, the more swerve (up to a point). Soccer balls are hit with side spin (and sometimes a touch of top spin) to make a side force, so they swerve”.

Finally, the Aerowtrac grooves may have an effect on erratic flight. Carré explains: “Any ball that has a pattern of grooves or seams could show erratic flight if it is spinning very slowly during its travel. Basically, the pattern of roughness that the air has to encounter as the ball travels is changing during the flight, so any side, up or down forces change, too.”

The Ordem 3 features a fuse-welded synthetic leather casing and a geometric 12-panel design, which Nike claims enhances the ball’s flight and allows pressure to be distributed evenly across the surface.

Carré points out that “the more ‘repeating’ the pattern and surface roughness of the ball, the more chance it will behave consistently, no matter what the ball orientation is, or how slowly the ball rotates. So the ‘drag’ and ‘consistent swerve’ effects will be more repeatable.

“If only the seams between panels contribute to roughness, then more panels equal more roughness. This was certainly the case years ago, but now manufacturers are also adding roughness by putting texture on the ball. You could theoretically make a ball out of one panel or two, but if you are adding texture, grooves or dimples, you will still have roughness (like a golf ball). The construction itself doesn’t control the roughness; the overall effect of seams and texture does. Roughness design used to be dominated by how a ball could be constructed (i.e. stitched leather, and later synthetic material patches). New ways of bonding and pre-shaping curved panels have meant there is much more freedom in the number and shape of panels, so manufacturers have started adding texture in almost any way they like”.

Considering future developments in ball design and whether the ultimate ball (in terms of flight accuracy) could ever be achievable, Carré comments that “all sports technology and equipment evolves over time. Usually a combination of new materials, new construction methods and better scientific understanding drives this evolution. Ultimately, products need to sell, but with sport, changes are also driven by a need for improved performance, or in some cases a governing body will step in to prevent a dramatic change that would ultimately alter the nature of the game.

“I don’t think any product can ever be as ‘accurate’ as possible (you can replace that with almost any adjective you like: ‘fast’, ‘hard-wearing’ etc), but what is true is that it becomes harder and harder to make improvements which are noticeable by the players.

“Secondly, the style of play can change and therefore different attributes are needed, which changes the design. An example of this is the evolution of field hockey. When the sport started to use synthetic pitches, the nature of the game changed completely, becoming much faster.

“In the future soccer may change to the extent that spectators want to see more goals and more exciting crosses and shots. It is growing very fast in the US and other parts of the world and these new markets could also drive these new needs.

“Currently, I think the main requirements from players are the same as they have been for a while: a fast-travelling ball that is controllable when kicked and swerves appreciably when you want it to (although goalkeepers may not agree), as well as performing consistently.

“‘Consistent performance’ can include how the ball performs in different conditions, such as high altitude or rain, over time (as it is repeatedly kicked) and between balls of the same design.”

It seems any youngster getting into soccer today should focus on becoming a striker, since the life of the goalkeeper looks set to become ever more difficult.