Why Hybrid strings? If you want the best of both worlds to combine the durability and spin potential of polyester with the playability and comfort of natural gut or a multifilament, the pick a hybrid combination. The majority of people now use the polyesters as a HYBRID by combining with a Synthetic gut or multi-filament. Federer uses a Hybrid Luxilon/Wilson mixture called Champions Choice, which is basically Luxilon Alu Power rough PLUS Natural Gut. Most people use polyesters on the MAIN strings and anything else on the crosses. Federer does it the other way around...with natural gut mains and Alu Power Rough crosses...but hey he can do what he likes and he does not have to pay for his strings. We would always recommend that the tougher string be used for the mains.