Why would a heavily inflated balloon and a tightly knotted balloon be deflated in a few days?

A well-inflated balloon and a tightly tied balloon will be deflated in a few days, because during this time, a certain amount of air contained in its volume will leave the balloon.

The material from which the ball film is made is not airtight.

And the molecules of the air mixture gradually “seep”, penetrate through the microlacunas, the micropores of the material – outward.

This process is rather slow, but within a few days its result becomes noticeable – the ball “softens”, turns out to be deflated.