There's One Crucial Reason Why Airplane Windows Are Designed Round

Whether you're the type of passenger who loves booking a window seat or someone who prefers to stay far from any reminders that you're flying 35,000 feet above ground, plane windows regularly play a role in plenty of travelers' journeys. But here's the thing: That curved frame has a much bigger purpose than simply letting you comfortably rest your head against the plane window (Spoiler alert: Even flight attendants recommend not doing this) or capture snaps of cotton candy clouds as you set off on your next getaway. After all, the rounded shape you see on pretty much every commercial aircraft today isn't just a style choice — it's actually an engineering solution that keeps planes and their passengers safe at cruising altitude without the risk of structural failure or dangerous pressure buildup.

And while most travelers don't necessarily think twice about the ins and outs of how an airplane works — we'll stick to browsing the in-flight entertainment or following the little animated map at most — the reality is that each piece and design element (no matter how small or unnoticeable) does a lot more than you might think.

When an aircraft climbs to cruising altitude, there's a major challenge that can affect passenger safety: maintaining a comfortable cabin pressure while the air outside becomes increasingly thin. Once the plane is up in the air, this dramatic difference between internal and external pressure starts to create a lot of stress on the airplane's entire structure — especially around any openings like windows. This, in turn, makes them more susceptible to damage or failure, which means that even the smallest design flaws can end up causing some pretty serious consequences.

However, these effects weren't always that clear. During the early days of commercial aviation — think back in the day, when smoking was still allowed on board and better seats with more legroom actually existed — planes flew at lower altitudes and windows were square. As the commercial aviation industry matured, airlines discovered that flying at higher altitudes could save money, due to the thinner air resulting in less drag. However, engineers hadn't fully grasped how the difference in pressure could negatively affect planes at these higher altitudes. This fault became devastatingly clear in the 1950s, when three de Havilland Comets — the first-ever commercial jetliners — fell apart mid-flight. In the end, an investigation concluded that the accidents happened as a result of metal fatigue, which concentrated around the corners of the square windows and caused them to crack under pressure, ultimately causing the fuselage to break apart and the planes to disintegrate.

Don't worry, though: Round airplane windows pretty much solved the issue of structural weakness. By getting rid of corners altogether, the circular shape of the window is able to distribute pressure evenly around the frame — preventing any single point from bearing the brunt of the pressure or buckling under too much stress. This breakthrough ended up transforming the physics of flying completely — making it safer for planes to fly higher than ever before.

Beyond that, the actual materials that make up airplanes and their components also evolved and adapted to high-altitude conditions. Nowadays, plane windows are made using multiple layers of acrylic rather than glass, which is both stronger and more durable at high altitudes. This, along with a small "breather" or "bleed" hole that helps manage pressure between those panes — and even prevents windows from fogging up — adds another layer of protection. At the end of the day, these small but crucial design choices come together to ensure that every window stays strong, secure, and reliable — even under extreme or challenging conditions.