This information about tennis balls comes from my buddy Joe
FACT #2: Felt balls pressurized or not – At this time, most manufacturers are going with low pressure (not pressureless) felt transition balls. The red level balls are so low pressure that they will only minimally lose pressure over time. This is why no company puts them in sealed and pressurized cans. The orange balls will slowly lose some pressure over time but, generally speaking, it will take many months and hardly be noticeable. The green level balls are about half the pressure of regular 14 psi (pounds per square inch) tennis balls and will “soften” the most over time. This is partially why we offer them in buckets and cans. Oncourt Offcourt offers the orange and green balls both in buckets and pressurized numbered cans.