Ever wondered why airplane windows have a small hole? Robbie Gonzalez from i09 recently set out to uncover the truth behind this peculiar feature, putting to rest any other speculative theories.

Gonzalez explored the reason behind the tiny hole found at the bottom of airplane windows, dismissing other ideas and explaining the purpose behind this design feature.

An airplane window is made of three layers: the outer pane, which acts as the main structural barrier; the middle pane, where the small hole is found; and the inner pane, which is closest to the passengers. Between the outer and middle panes is an air gap, creating the “two-pane air-gap design,” which is engineered to withstand atmospheric pressure.

At an altitude of 35,000 feet, the outside air pressure drops to 3.4 pounds per square inch. To ensure passengers can breathe comfortably, the cabin pressure is kept at around 11 pounds per square inch. Gonzalez points out that “The greater the pressure difference between the inside and outside of the plane, the greater the stress on the plane’s structural elements, including the windows.”

The small 'breathing hole' in the window serves as a pressure-regulating valve. It allows the air pressure between the cabin and the gap between the outer and middle panes to balance, ensuring that only the outer pane bears the full pressure. This design leaves the middle pane free for emergency situations.

For a deeper dive into the significance of the tiny hole and its important role, take a look at Gonzalez’s article on i09.