My wife, my student, hits the ball nicely for an hour but her racket starts twisting once the sweat starts to build up. Towels don't help nor does a new tacky overgrip. Firming her grip helps but just a little bit because of off center shots. This Prince hand/grip powder though once applied to her hand allowed her to keep her racket from further twisting and gaining back full control of her shots have made her enjoy many hours in the court. She calls this her magic powder.