Have you ever taken a bag of potato chips (or crisps, if you're British) on a flight, and they expand and possibly even pop midflight? You're not alone. In this guide, we will attempt to explain why potato chip bags expand, why they don't always return to the same size, whether bags of chips will burst midflight and other questions you may have relating to snacks on a flight!

Why do chip bags expand?

Potato chip bags generally expand because of a difference in pressure inside and outside the bag. This is known as a 'pressure differential' and is explained through the gas law in physics, which says that the pressure and volume of a gas have a negative correlation, meaning when one increases, the other decreases.

In the event of an aircraft gaining altitude, the gas inside the chip bag will expand as the atmospheric pressure (the pressure outside the bag) decreases. Potato chip bags increasing in volume is not a phenomenon limited to airplanes. For example, people going on hikes may have a similar, yet less pronounced experience, as you are indeed gaining altitude, but at a much lower rate.

Why doesn't it return to its normal size on landing?

After landing at a different airport, you may expect the bag of chips to return to "normal" - however, due to the altitude of the airport and other conditions, there may still be a pressure differential which can explain the increased size. Other factors which may affect the size of the photo chip bag include the temperature at the location, as the gas law also describes temperature as an important component in the equation.

However, as opposed to pressure and volume having a negative correlation, temperature has a positive correlation, meaning that if the pressure or the volume increases, then temperature will also increase.

Moreover, what is important to consider is that the pressure differential should be measured against the factory where the bag of chips was sealed, and not the initial departure airport. Therefore, while there may not be a difference in altitude between the two airports, there could nevertheless be a difference between the landing airport and the potato chip factory.

Will the bag pop?

Potato chip bags, in particular well-designed ones, generally will not pop. Food pouches are said to only burst when the difference in pressure inside and outside the pouch is too great. A small pressure differential usually does not have a huge effect on the food pouch, as they are designed to withstand a pressure differential of up to several atmospheres.

In addition, the pressure inside potato chip bags is simply too low even to cause a rupture, meaning that while the potato chip bags will inflate, they will not burst as the pressure differential between the content of the bag and the atmospheric pressure is not great enough.

The bottom line

While the TSA in the United States does not prohibit passengers from carrying potato chip bags, good advice is to simply bring other snacks, such as cookies, granola bars or candy, as they tend to be less messy on flights!

Sources: Stand Up Pouches, Vending Pro Service, Physics Stack Exchange, Quora.