# What's That Hole at the Bottom of Airline Windows? ![[images/Whats That Hole at the Bottom of Airline Windows.webp]] **Creator:** The Overview Effekt · **Published:** Oct 16, 2015 · **Length:** 0:49 · [Watch on YouTube](https://www.youtube.com/watch?v=uq9Fc3rzNyc) ## Outline ### 00:00 Introduction - The question: why do airplanes have that little hole at the bottom of the window? ![[images/Whats That Hole at the Bottom of Airline Windows-t0002.webp]] ![[images/Whats That Hole at the Bottom of Airline Windows-t0006.webp]] ### 00:08 Window construction - Most airline windows have three parts. The **inner layer** is a dust or scratch cover that keeps people from poking or scratching the real window. - Behind it are two panes that form the main window. Each is a half-inch-thick piece of plexiglass, and they are separated by about half an inch of air. - The **middle pane** has the hole, sometimes called the **breather hole**. ![[images/Whats That Hole at the Bottom of Airline Windows-t0017.webp]] ![[images/Whats That Hole at the Bottom of Airline Windows-t0021.webp]] ### 00:24 Purpose #1: anti-fogging - The hole lets warm cabin air in between the two panes. This keeps the outer window from frosting or fogging up from the very cold air outside. ![[images/Whats That Hole at the Bottom of Airline Windows-t0025.webp]] ![[images/Whats That Hole at the Bottom of Airline Windows-t0030.webp]] ### 00:36 Purpose #2: pressure regulation - As the plane climbs and descends, the air pressure on the window changes. The breather hole keeps the pressure between the two panes the same, so they don't implode or explode. ![[images/Whats That Hole at the Bottom of Airline Windows-t0037.webp]] ![[images/Whats That Hole at the Bottom of Airline Windows-t0046.webp]] ## Things Mentioned ### Aircraft parts - The cabin window assembly: the inner scratch/dust cover, the inner (middle) pane with its breather hole, and the outer pane; the plexiglass panes (each ~½ in thick, with a ~½ in air gap) ### Physics concepts - Condensation and frost from cold outside air; changes in cabin and outside air pressure during ascent and descent; pressure equalization ### Tools and sources - Per the description: airplane manuals and aircraft mechanic forums. Animated in Adobe After Effects (from the video tags). - The creator's note: you could argue the hole also preserves the structural integrity of the outermost pane, which he feels his explanation implies. ## Biographies - **The Overview Effekt**: a YouTube channel known for 3D-rendered maps and visualizations of spaceflight and sci-fi. This 2015 short is one of its early animated trivia explainers. No other people are mentioned.