The pressure held in the ball is over and above ambient air pressure
So a ball inflated to 6psi is technically closer to 20.5psi (ambient (~14.5) plus 6) – but ambient air pressure is assumed
When a ball is ”flat”, it's merely holding air at ambient pressure, but the structure of the ball doesn't want to stay ball-shaped without the additional air pressure
July 11, 2020 at 08:10AM
via reddit https://www.reddit.com/r/explainlikeimfive/comments/hp8uhd/eli5_whats_in_a_ball_when_it_is_flat/fxnq1lu?utm_source=ifttt