Roger Federer is continuing his experiment with a blacked-out 98-square-inch head Wilson frame, but is unsure whether he will still be using it when he arrives in North America for the summer hard court season.

Federer, who previously played with a 90-square inch Wilson, used the new frame last week in Hamburg and is also trying it out it this week at the tournament in Gstaad. The Swiss fell to Argentine qualifier Federico Delbonis in the Hamburg semifinals using the racquet.

"So far, I'm happy with this change,” Federer told reporters. “But I need many hours on the court to see. I haven't yet taken the decision on whether to use it in the U.S. I still need to think it over. There are players who have experienced problems when they changed racquets, Fernando Verdasco, and to some extent, Novak Djokovic."