Airplane windows are made of stretched acrylic, not glass, since it’s both stronger and more lightweight than glass.

Airplane windows need a strong and lightweight material to ensure they aren’t easily cracked or broken, as a cracked or broken window could cause an emergency by reducing the pressure and oxygen levels of the plane.

Airplane windows may be strong, but they can still be shattered with bullets or an axe.

In fact, many planes keep an axe on board for breaking the windows if there’s an emergency. 

Why Airplane Windows Are Designed the Way They Are

Airplane windows are designed the way there are for several reasons.

  • Airplane windows are constructed to reinforce the plane’s structural integrity during flight.
  • Having interlocking windows ensures that the chances of a window break are reduced. 
  • Airplane windows are rounded because they are harder to crack. Planes used to have square windows, but they’re much easier to crack. 
  • It’s important to prevent airplane window cracks, since a broken window would cause the airplane cabin to lose pressure and oxygen. 

Thickness of Airplane Windows

Airplane windows are generally 15 mm thick.

The inner pane is often 5 mm thick, while the outer one is 10 mm thick. But, the exact thickness of a plane’s windows depends on its type and the manufacturer.

The outer panes carry the pressure of the aircraft during flight, while the inner panes are a fail-safe if the outer ones break. 

Airplane Windows Are Extremely Strong

Airplane windows, especially the cockpit ones, are extremely strong.

The cabin’s windows experience a force of 0.5k per square cm of glass when a plane is cruising.

The average cabin window is 40 cm by 50 cm, so it experiences an excess of 1 metric ton of force while cruising. 

Airplane windows have to be strong to prevent breakage, which could depressurize the airplane, causing an emergency. 

Cockpit windows are usually even stronger.

Airplane Windows Aren’t Bulletproof Though

Airplane windows are not bulletproof.

The stretched acrylic they’re made of is a light and strong material that resists physical impact, but is not strong enough to withstand bullets. 

It’s Possible to Smash a Plane Window

Airplane windows are designed to be extremely resistant to physical attacks, but can still be smashed.

However, smashing a plane window requires tremendous force – over 1,750 lbs.

The easiest way to smash an airplane window would be to strike the window’s corner with an axe. Striking the window’s corner would break away enough pieces to let you remove the rest of the window. 

Some planes even have an emergency axe onboard to break the windows during an emergency. 

How Airplane Windows Are Tested

Airplane windows are primarily tested with bird strike tests, since the biggest danger to airplane windows is from bird strikes.

Commercial airlines use windows that are rated to withstand a four-pound bird strike between 250 and 350 knots. 

Aircraft windows are also tested for pressure, temperature control, and chemical resistance.

Airplane windows must also be resistant to hydraulic fluid, jet fuel, and abrasions, like rust or rain erosion. 

Airplane windows may also be tested in other conditions where the fail-safe aspect of the window’s design is tested. 

Why Airplane Windows Are Round

Airplane windows are round for safety, since round windows are harder to break than square ones.

Rounded windows better distribute the pressure exerted on the windows, which reduces the chances of a crack caused by changing air pressure. 

Related: How Far Can You See from an Airplane Window?

Why There is a Little Hole in the Window

The little hole in plane windows releases moisture and helps balance the pressure difference between the plane’s cabin and the outside.

It’s important to balance the difference between the plane’s cabin and the outside for safety reasons. 

The hole also releases moisture and stops frost and condensation from forming on the window, which keeps the view clear for passengers. 

What is the Cockpit Windshield Made Of?

Cockpit windshields are made of a laminated structure containing layers of glass, polycarbonate plastics, and acrylic bonded by layers of polymeric bonding material.

The design of cockpit windshields provides increased strength without increasing unnecessary weight.

Related: Why is a Cockpit Called a Cockpit?

In conclusion:

  • Airplane windows are made using stretched acrylic.
  • Airplane windows are designed to withstand extremely high pressures during flight.
  • The average airplane window can withstand over 1,750 lbs of force and is 15 mm thick.
  • The windows are rounded for safety reasons, since rounded windows are harder to crack.
  • A crack in the airplane windows could potentially cause an emergency since it would reduce the plane’s pressure and oxygen levels.
  • That being said, airplane windows aren’t indestructible. They can be shattered with bullets or an axe.
  • The easiest way to crack an airplane window is to crack its side to break enough pieces from it to remove the rest of the window.

Helen Krasner holds a PPL(A), with 15 years experience flying fixed-wing aircraft; a PPL(H), with 13 years experience flying helicopters; and a CPL(H), Helicopter Instructor Rating, with 12 years working as a helicopter instructor.

Helen is an accomplished aviation writer with 12 years of experience, having authored several books and published numerous articles while also serving as the Editor of the BWPA (British Women Pilots Association) newsletter, with her excellent work having been recognized with her nomination of the “Aviation Journalist of the Year” award.

Helen has won the “Dawn to Dusk” International Flying Competition, along with the best all-female competitors, three times with her copilot.