For several decades, the yellow jersey was made from wool. Its high performance properties offered the elite athletes protection from sun and extreme temperatures, managed sweat, and the riders firmly believed in the pureness of the fiber.
Synthetics were introduced in 1947 by Tour de France sponsor, Sofil, who made an artificial yarn. Previously, riders added the name of the team for which they were riding by attaching a panel of printed cloth to the front of the jersey with pins.
When Louis Bobet won the yellow jersey, he passionately refused to wear Sofil's synthetically made jersey, because he believed that cyclists NEEDED wool for proper hygiene and protection from the long days of sweating in the heat. Moreover, he felt that synthetics made riders sweat excessively because they did not absorb moisture or breathe.
Jacques Goddet, long standing director of the Tour de France, recollected, "It produced a real drama. Our contract with Sofil was crumbling away. If the news had got out, the commercial effect would have been disastrous for the manufacturer. I remember debating it with him a good part of the night. Louison was always exquisitely courteous but his principles were as hard as the granite blocks of his native Brittany coast."
Sofil had to produce a wool jersey overnight, complete with their logo. It was the only way that Bobet would wear the yellow jersey.