Here it is-
June 19, 2011
But the strings are where the real breakthroughs have come in the past decade. The development of polyester strings has changed the game by allowing players to take bigger cuts without bigger risks. Nadal switched to a new type of Babolat co-poly string called RPM Blast in January 2010 designed to help improve spin.
Federer and Djokovic use a blend of polyester strings and natural gut. They use gut in their main, vertical strings and polyester in their cross strings, the opposite of what most players do.
“When Roger went this way and started racking up Slams, there was a period when everybody started switching and then they all went back,” Wilson’s Ron Rocchi said. “The theory is that you put poly in the mains to get durability, and gut in the crosses helps playability. But Roger was stringing rackets so often anyway, he didn’t care about durability. He went for a different feel on the string bed, and it comes from the fact he is stringing a very small head size at a very low tension.”