Let us assume that you’re going to take a flight, now among the first questions that pop into your head is whether to go for a window or an aisle seat.

Despite very few people, a curious traveller will often opt for a window seat – partly to take in fluffy clouds and meandering rivers and roads, but also so that they can fall asleep against a solid surface rather than a stranger.

If you’re a regular window seater, then you’ve probably spotted the small hole at the base of the glass window itself – and quite possibly the small specks of frost that sometimes form around it.

Further, Zooming in:

This hole is technically called as “breather hole”, being a cause for concern, it’s actually, probably unsurprisingly, there to keep passengers and crew safe.

Marlowe Moncur, director of GKN Aerospace technology revealed that the hole’s job is to “allow pressure to equilibrate between the passenger cabin and the air gap between the panes.” This, in turn, enables the cabin pressure to be applied to the outside-facing pane.

At cruising altitude, the pressure falls so low – 3.4 pounds per square inch, in fact – that a person wouldn’t be able to survive it. For this reason, cabin pressure is kept at approximately 11 pounds per square inch for the duration of the flight, and it’s because the windows are designed so cleverly that they’re able to withstand the disparity.

The plane windows are actually made up of three panes from inside. The outer and middle ones effectively contain the variance in pressure between the cabin and the sky outside, with the breather hole ensuring that only the outer pane withstands the pressure.

Because, then, there is effectively a pair of panes on the outside – one facing outside and another in between this and the inner pane – the window is actually pretty safe.

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