WILSON US OPEN TENNIS BALLS/3pcs/ Tennis balls pressurized for all court surfaces. Description:# Official ball of the Polish Association Tennis# since 1978 the official ball of the Grand Slam US OPEN# has additional felt increasing the strength of the ball# made of the highest quality felt (large mixture of wool)# technology nCODE- limiting the loss of air penetrating from the inside of the ball to the outside (the pressure stays at the correct level longer than in traditional balls-the ball bounces more predictably can: 3 pcs.Modern technology ensures increased strength, consistency. All balls use the top quality solutions to be in the best possible reduce the loss of air from the ball to the outside. Thanks to the new-of-the-art technology nanoparticles make this loss minimal. This makes the pressure stays at its original level and causes the ball to bounce more predictably.