A sealed bag of potato chips often appears dramatically inflated when taken to a higher elevation, such as on an airplane or a mountain. This noticeable puffiness is a direct and predictable result of fundamental physics. The phenomenon highlights the sensitivity of gases to the external air pressure, which changes significantly with altitude.
The Relationship Between Altitude and Atmospheric Pressure
Atmospheric pressure is the weight of the column of air pressing down on a particular location. At sea level, this column is tallest, and pressure is at its maximum, typically around 14.7 pounds per square inch (psi). Air molecules are densely packed near the Earth’s surface because gravity pulls the majority of them downward.
As one ascends to a higher altitude, the column of air above becomes shorter, and the air molecules become less dense. The atmospheric pressure decreases significantly. For instance, at an altitude of about 10,000 feet, the external air pressure is roughly 30% lower than it is at sea level. This drop in external force is the single factor that initiates the chip bag’s expansion.
How Fixed Internal Pressure Causes Expansion
A bag of chips is typically sealed at a manufacturing facility near sea level, trapping air or an inert gas like nitrogen at that initial pressure. Once the bag is sealed, the internal pressure becomes fixed, regardless of where the bag is transported.
When the bag moves to a higher altitude, the external atmospheric pressure drops, but the internal pressure remains the same. This creates a pressure differential where the internal pressure is substantially greater than the external pressure. The trapped gas molecules push outward against the flexible plastic film with greater force than the surrounding air pushes inward.
Gases naturally expand to fill the available volume, causing the sealed bag to act like a balloon. The greater internal force increases the bag’s volume until the outward pressure is either equalized by the lower external pressure or the physical resistance of the bag material prevents further expansion.
What Happens When the Pressure Differential Becomes Too Great
The expansion of the bag is limited by the structural integrity and flexibility of its multi-layered plastic film. If the altitude gain is too rapid or too high, the pressure difference across the bag’s surface can exceed the material’s failure point. When the outward force of the expanding gas surpasses the material’s tensile strength, the seal or the film will rupture, causing the bag to burst.
Manufacturers are aware of this altitude-related risk, especially when shipping products across mountainous regions or by air. To mitigate the risk of bursting, some companies package their chips with slightly less gas or partially vacuum-seal them for high-altitude markets. Most bags are also flushed with nitrogen, which preserves the chips by displacing oxygen and provides a cushion to prevent the fragile contents from being crushed during shipping.