After reading Rain's recent piece on the manufacturing of ping pong balls I began to wonder how the balls for other sports are made. Tennis balls came to mind because Wimbledon is underway.
I poked around and found manufacturing videos from 1961 and 2015. My take from watching them is that little changed in that time.
The process still involves pressing piece of rubber into semi-spherical shapes, vulcanizing them, joining them into spheres, and then covering them with felt. Parts of the process have been automated but tennis balls still require a fair amount of human labor .
The 2015 video shows the manufacturing process at Wilson's factory in Thailand. The 1961 video shows balls being made for Wimbledon at Slazenger's former plant in England . Slazenger still makes tennis balls but they're now produced in the Philippines.