The Real Reason Why Airplane Windows Have Holes

Wilbur and Orville Wright—the brothers credited with piloting the first successful flight in history—had to feel the wind on their faces. Their modest aircraft, a wooden biplane made of spruce and ash covered by cotton muslin, was open to the outside air. Fortunately, their history-making flight in 1903 lasted just 12 seconds and barely reached 10 feet off the ground. Today’s commercial planes spend most of their time at 30,000 feet (or more) where the temperature hovers around -40 degrees Fahrenheit, and temps as low as -70 degrees aren’t unheard of. For that reason, we need insulated aircraft to keep from freezing to death. While we don’t get the same killer views the Wright Brothers had in their open-air design, we can book a window seat. And if you’ve ever sat in one and noticed that the window has a tiny hole in the bottom of it, hopefully you didn’t panic. It’s not a manufacturing mistake. It’s an intentional feature that serves two key purposes—and it even has a special name. 

“Those little holes are called breather or bleed holes,” RD Johnson, vice president of safety at Jet Linx, tells Travel + Leisure. Airplane cabin windows aren’t made of glass; they’re typically made of three or four layers of plexiglass (which is a bit of a misnomer since it’s actually a form of plastic) or stretched acrylic. There is one bleed hole per window, and it’s usually found in the center at the bottom of the window. If you’ve ever placed your finger over the hole, you’ll notice that no air comes in or out. That’s because the hole doesn’t go all the way to the outside—it’s just in the center pane(s) between the inner and outer panes. 

In addition to flying long distances, planes cover a lot of ground in terms of altitude. After climbing, most commercial planes cruise at around six to seven miles above Earth before descending. As the altitude changes, so does the pressure. According to Brent Wouters, who got a master’s degree in aerospace engineering before becoming CEO of Jet Linx, “At different altitudes, the pressure differential between the air in the gap between the pressurized cabin (interior window) and the outside changes substantially.” Wouters tells T+L that these holes are necessary because they absorb the massive pressure differences.  If the windows were hole-less, they’d be at a greater risk of cracking. In the event that a cabin window cracks, the hole ensures that the inner pane breaks last. 

Fortunately, airplane cabin windows seldom break. Aircraft mechanics routinely inspect windows, and if they show any signs of wear or tear that could be dangerous, they swap them out. Furthermore, if a window cracks or breaks mid-flight, cabin crew are trained to assess the situation and act accordingly. In 2024, an All Nippon Airways flight traveling in Japan had to return to its departure airport when a cockpit window cracked mid-flight. Still, a spokesperson for the airline issued a statement saying, “The crack was not something that affected the flight’s control or pressurization.”

The secondary purpose breather or bleed holes serve is to keep windows clear. “The hole allows moisture to evaporate,” explains Wouters. “If it were sealed, moisture from condensation would accumulate, and the window would be useless.” So you can thank those tiny holes for keeping your bird’s-eye view clear and condensation-free.