The Wilson Champions Choice Duo Hybrid Tennis String is the string of choice of the great Roger Federer and combines the power and feel of Wilsons Natural Gut with the durability and spin of the Luxilon Alu Power Rough. Mr. Federer uses Natural Gut in the mains and Alu Power Rough in the crosses for a softer feel and superb playability. If players are looking for better durability then use Alu Power Rough in the mains.