How does breathing in and out of a paper bag create vacuum? As soon as you inhale, the atmospheric pressure collapses the bag. Bellows are different because the

How does breathing in and out of a paper bag create vacuum? As soon as you inhale, the atmospheric pressure collapses the bag. Bellows are different because they can hold their shape: if you seal all the ends and then expand the bellows, you will have vacuum and the 1atm of pressure trying hard to stop you from doing that. The same with hot air balloons, there is no vacuum at play there, unless I'm miss-understanding what you're saying.