Answer and explanation:
As we know, inside the bag of potato chips there is also air. Air is, of course, composed of several gases, such as oxygen, nitrogen and carbon dioxide. When the atmospheric pressure is high, the volume of gas is reduced. Therefore, if the pressure is lowered, the volume increases. That is why the bag gets puffy. You've taken it from a place with higher atmospheric pressure to one where it is lower, so the gas will expand.
