# Tennis balls **URL:** \ **Category:** Factual Questions\ **Created:** [July 29, 2001, 10:40am UTC](https://boards.straightdope.com/t/tennis-balls/74153 "2001-07-29T10:40:06Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![zeroth](https://avatars.discourse-cdn.com/v4/letter/z/839c29/32.png) [@zeroth](https://boards.straightdope.com/u/zeroth)\ **Post date:** [July 29, 2001, 10:40am UTC](https://boards.straightdope.com/t/tennis-balls/74153/1 "2001-07-29T10:40:06Z")
Recently I bought a tube of three tennis balls, and much to my surprise, they were vacuum-sealed. [Managed to cut my finger on the sharp edge of the lid, as well. LAWSUIT! :D] Anyhoo, I just figured someone here might know why they vacuum-seal tennis balls. Is it to keep the rubber from drying out? That’d be my guess but I’d like to be sure. ---
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [July 29, 2001, 12:01pm UTC](https://boards.straightdope.com/t/tennis-balls/74153/2 "2001-07-29T12:01:14Z")
The first return on entering “Vacuum tennis balls” is: [http://van.hep.uiuc.edu/van/qa/section/Cool\_stuff\_about\_Air/Pressure/908135162.htm](http://van.hep.uiuc.edu/van/qa/section/Cool_stuff_about_Air/Pressure/908135162.htm) I’m sorry that I don’t know the coding to make that cleaner. I believe that is all. ---
**Author:** ![barbitu8](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@barbitu8](https://boards.straightdope.com/u/barbitu8)\ **Post date:** [July 29, 2001, 5:00pm UTC](https://boards.straightdope.com/t/tennis-balls/74153/3 "2001-07-29T17:00:42Z")
Tretorn used to package 4 tennis balls in a box that were not air pressured. They were harder and lasted a pretty good time without any air pressure. I don’t know how they did it, but you may want to search under Tretorn. I don’t know if they still exist. There is sold a little tube in which you can stick the balls into after you’ve open the tennis can, and then pressurize it by turning a screw or some such gizmo. I have an older version in which the balls sit in little cubby holes in a round gizmo and the top is tightened with a turnscrew. It helps a little, not much. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 29, 2001, 7:52pm UTC](https://boards.straightdope.com/t/tennis-balls/74153/4 "2001-07-29T19:52:02Z")
They’re not actually vacuum-sealed, they’re pressure-sealed: The air in the canister is at a higher pressure than outside, not lower. Apparently, many or most tennis balls have slow leaks (if “leak” is the right word; I think it’s an osmotic process), but if you keep their environment pressurized to the same level as the interior, there’s no problem.