The balls used in men’s and women’s tennis are different.
(They are the same size, weight and pressure: between 2½ and 2 5/8 inches (6.35 and 6.67 cm) in diameter and weighing between 2 and 2 1/16 ounces (57.7 and 58.5 grams) but balls used by men have an extra-duty felt covering, which increases air resistance and slows the overall speed. Women players use regular-duty felt.
Professional tennis player Bob Bryan, who uses both kinds of balls on the men’s and mixed doubles circuit, believes he can add around six mph to his serve when playing with the women’s regular balls.
It is very difficult to write about this without sounding silly.)