Federer hybrids the Natural Gut on his main strings with the Alu Power Rough on his Cross strings。
Alu Power Rough should be strung 5-10% lower than your normal tension according to the manufacture advice.

-I've read somewhere (not necessarily a reliable source) that Federer gets his ALU crosses strung 1-2 lbs lower than his mains. (this would seem to make sense, because if you assume that a typical tension for a hybrid job with any other strings might be 56lbs mains/ 60 lbs crosses, then adjust 10% for luxlion to 56 lbs mains /54 crosses