Airplane windows are sealed primarily to maintain a pressurized environment inside the cabin, which is essential for human survival at high altitudes. At a cruising altitude of 35,000 feet, the air pressure outside is so low that a human would lose consciousness within seconds; therefore, the cabin is "inflated" with compressed air to simulate a safer altitude. The windows consist of three layers of high-strength acrylic: the outer pane (the thickest) takes the full force of the pressure difference, the middle pane serves as a fail-safe backup, and the inner pane (the "sneeze guard") protects the system from passenger contact. You may have noticed a tiny hole at the bottom of the window—this is called a "bleed hole." It allows air to circulate into the gap between the inner and outer panes to equalize the pressure, ensuring that only the strong outer pane is carrying the structural load. This clever piece of engineering also prevents moisture and frost from building up between the layers, keeping your view of the clouds clear while ensuring the "pressure vessel" of the airplane remains perfectly intact throughout the flight.