Ilford sealing wrapper for 120 roll film

I was playing with a sealed packet of delta 400 before opening it and noticed that when I squeeze it, air comes out of the wrapper. It seems to be true also with another two rolls I had lying around of different Ilford emulsions. Not so with Kodak. It seems to be actually sealed. So what's the point of Ilford's wrapper if it isn't sealed? Or did all my wrappers "pop"?

To me it is not correct for principle.

However, how big must a hole be to allow for gas/vapour exchange within the expiry date? I got no idea.

And I doubt anyone here has... Physicists come up!