This Is Why Airplane Windows Have Holes
The answer will surprise you.
There are a number of things most travelers look for in a plane: cleanliness, quietness, and some measure of certainty that the vessel propelling them through the skies is airtight. However, while betting on a lack of visible grime and crying babies is always a crapshoot, those little holes in the airplane windows can make even the most intrepid traveler more than a little nervous. So, why are they there, anyway?
From the inside, a plane's windows may seem to have just an interior and exterior pane, but there are actually three panes between you and the icy-cold air at 30,000 feet. There's the pane closest to you, informally known as the scratch pane, then the middle pane, which contains the so-called "bleed hole" or "breather hole," and, on the plane's exterior, there's a third pane.
When you hit cruising altitude, the difference between the pressurized cabin and the low-pressure air outside is pretty significant—potentially enough to break a window, in fact. However, the use of the bleed hole helps regulate the pressure between the window panes, keeping them stable, despite the disparity between the plane's internal and external pressure. As such, the bulk of the pressure is then applied to the window's outer pane. While this may seem risky, it actually ensures that, should the exterior window crack, the two interior panes can still keep you safe from the elements outside.
But wait! That's not the only advantage of the little window hole. The bleed hole also helps balance the difference between the plane's interior and exterior temperatures, reducing condensation and giving passengers a clear bird's-eye view over the landscape. And for more insider tips and tricks, check out the 20 Shocking Secrets Flight Attendants Won't Tell You.