AMERICA'S #1 SELLING BALL: The product of 100 years worth of testing and perfecting; Penn produces the best selling line of tennis balls in America. GREAT FOR BEGINNERS: The QST 36 kids' foam tennis ball features a higher density for controlled bounce and reduced speed. An ideal beginner ball for playing on a 36' court. MASTER THE BASICS: With a red and yellow 2-tone felt design that allows players to easily track spin, Penn junior tennis balls are great for young players still mastering their hand eye coordination. OVERSIZED: An ideal first tennis ball, the QST foam has an oversized diameter for simplified training and practice. USTA APPROVED: A high quality and consistent ball, Penn QST is approved by the USTA for the 10 and Under Tennis Program.