A few things every player should know when purchasing tennis balls.
By John Levey / Copyright: TENNIS July 2006

Pick up a can of Wilson US Open balls or Gamma ProTour and you will notice the words “Extra Duty” or “Regular Duty” written on the can without any explanation as to the meaning. Some other brands are more forthcoming, but you don’t have to go looking for answers. What this refers to is the thickness of the felt surrounding the ball.

Extra-duty felt is thicker, which gives it added durability for use on hard courts. Play with this type of ball on clay and the dirt will slowly collect on the felt, causing the ball to fluff up and play like a muddy brick. That’s why a regular-duty ball, with its tightly woven felt, is a smarter choice on clay. Similarly, if you play with regular duty on a hard court, it will get beaten up in no time. Occasionally you will find an all-surface ball that’s designed to be a balance between the extra and regular-duty balls.

Photo: Pen tennis ball-did you know? Penn is the official choice of the USPTA and the only ball manufactured in the U.S.