With patented technology, Tretorn Micro X tennis balls are the original high-performance micro cell ball — powered by 700 million air-filled micro cells for improved playability. The exclusive high visibility flex-felt provides the best core dynamics and durability. Due to its construction, the Tretorn Micro X ball is well suited for play in colder climates, at high altitude and ideal for all court surfaces, including lower bouncing surfaces. The Tretorn Micro-X balls are recognized worldwide as the superior tennis balls available today for use with tennis ball machines.