This experiment features a PVC pipe with a closed valve in the middle has two balloons attached to either end. One balloon is blown up fully; the other is blown up only a little.
The big balloon got bigger and the small balloon got smaller. This is because the smaller balloon has a higher pressure. This is due to the surface tension of the balloons. This can be found in the Young-LaPlace equation. Have you ever noticed that it is the hardest just to start blowing up a balloon, then it gets easier? This also applies to a baby's first breath being difficult, as all of the alveoli are deflated.