The author of Mathletics: A Scientist Explains 100 Amazing Things About the World of Sports, tells us exactly how polyurethane swimwear works and why it's not allowed at the 2012 London Olympics.

The world of swimming has recently emerged out of a very difficult period in which it had to come to grips with the role of new technology in the sport. We are used to technical improvements in pieces of equipment like tennis racquets, fiberglass vaulters’ poles, and golf clubs changing performance levels, but the appearance of whole-body polyurethane swimsuits has taken the issue to another level. Swimmers have always taken steps to reduce the drag on their bodies through the water. All body hair was shaved off ahead of major competitions, and sleek swimming caps were used to remove any drag from head hair. But the new swimsuits took these measures a whole lot further. They were made from an extremely thin layer of foamlike material that enclosed tiny pockets of gas that made the swimmer wearing the suit to be far more buoyant. As a result, swimmers floated higher in the water and were subject to less drag. The suits in effect pushed water away from the swimmer’s body and were therefore dubbed hydrophobic.

The drag on the human body moving in water is around 780 times larger than the drag when moving in air, so there is considerable advantage to getting as much of the body above the water level as possible. These suits also made the body shape very smooth and hydrodynamic. Instead of the joint between a man’s body and the waist cord of his swimsuit adding extra drag, there was now a seamless, wrinkle-free, low-resistance outer shell skimming through the water. Tiny fibers on the surface of the suit could move to keep the shape streamlined and its texture smooth as the body shape changed through the stroke. Overall there was the possibility of an 8 percent reduction of drag on a swimmer. There are downsides, however. Putting on one of these thin-film polyurethane suits takes about half an hour, so you wouldn’t want to use one in every early-morning training session! And they don’t last long: you will need a new one after every few races, and they are not cheap, costing about $500 each in America.

The result of all of this was the erasure of outstanding world records by performances that were intrinsically inferior. Twenty new world records were set at the World Swimming Championships in Rome during July 2009 alone. Not all swimmers were wearing these suits at championships, though, and races were becoming manifestly unfair. Those who wore them were entering a technological arms race as different sponsoring companies tried to produce superior suits for their swimmers. Moreover, the sponsorship deals that top swimmers had entered into prevented them from switching to the best suit if it was made by a rival company.

The world’s best swimmer, Michael Phelps, seemed to concentrate everybody’s minds when he suggested, via his coach, Bob Bowman, that he might boycott all future international competitions where the new suits were allowed because they were distorting the sport. Swimming and the International Olympic Committee seemed to be faced with a future without a competitor who had won 14 Olympic gold medals—more than any other sportsman or -woman in history.

Not surprisingly, then, in 2010 there was a ban on buoyant polyurethane swimsuits. An uncompromising American proposal to return to allowing only textile suits was passed with 180 nations voting for it and only seven against. While FINA didn’t nullify past records that were set by athletes using polyurethane suits, they were “starred” in the same way that records set at high altitude are marked separately in the record books of track and field.

Excerpted from Mathletics: A Scientist Explains 100 Amazing Things about the World of Sports by John D. Barrow. Copyright 2012 by John D. Barrow. With permission of the publisher, W.W. Norton & Co., Inc.