Featuring patented technology, the Tretorn Micro-X Pressureless Bag of 72 tennis balls offer high performance and improved playability. These pressureless tennis balls are powered by 700 million air-filled micro cells that maintain bounce over time. The exclusive high visibility flex-felt offers strong core dynamics and durability. Due to its construction, the Tretorn Micro X pressureless ball is well suited for play in colder climates, at high altitudes, and all court surfaces--even lower bouncing surfaces. Recognized worldwide as the superior pressureless tennis ball, the Tretorn Micro-X is perfect for practice and tennis ball machines! Approved by the USTA Micro Cellular patented technology creates a highly playable pressureless ball that maintains performance over time. Includes yellow and white felt pattern