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I've always wondered, what are those dual-layered (bonus: sometimes they have a little <2mm hole, why is it there?) windows commercial jets put next to their seats made of?

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2 Answers 2

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Generally aircraft windows are made of what we colloquially call "plexiglass" of some kind (Lexan polycarbonate is common in light General Aviation aircraft, acrylic plastics are also used). This material is light, relatively strong (not shatter-proof, but it'll take a moderate beating) and has decent optical properties.
Its major drawback is "crazing" -- hairline cracks on the surface of the material that form over time from dirt, stress, temperature, UV exposure, and the like.


Bonus answer: The little hole serves a couple of purposes, but the biggie is pressure relief/equalization. This gets discussed over on airliners.net a lot and they've covered it pretty thoroughly.

Basically the hole ensures that the cabin pressure is pushing against the outer (primary, usually thicker) sheet of plexiglass, which is plug-wedged into the fuselage structure and can't go anywhere.
Should the outer pane be damaged the hole will also theoretically bleed cabin pressure off at a controlled rate - though how successful that equalization is would depend on your altitude (and thus the pressure differential between the cabin and the outside air) and the degree of damage to the outer pane.

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As for shattering, it only depends on thickness - fighter aircraft feature moderately bullet-proof canopies (not even talking about birdstrike) and all the huge show aquaria sport PMMA panes. –  yankeekilo Jan 7 at 18:40
    
I wonder about the pressure relief thing, especially concerning pressure loss - not sure if this hits the spot (see also this). –  yankeekilo Jan 7 at 18:45
    
@yankeekilo Yup - thickness and design (you can get layered polycarbonate or acrylics which basically function like kevlar) - if you've been to a bank in the US recently you've probably seen the wall of bullet-resistant plastic between you and the tellers. Re: the hole, I'm not sure I completely buy the pressure transfer/relief thing, but I'm not sure I completely buy the condensation thing either (why not fill the middle chamber with dry nitrogen before sealing them together?) I suspect it's a little bit of both honestly, or possibly something else entirely. We need a jet A&P in here! :) –  voretaq7 Jan 8 at 2:54
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The cabin-side screen is just a flimsy, easily replaceable thing that is used to protect the actual window and add a bit of thermal insulation. It does not form any kind of hermetic cavity with the window, too, but sits inside the pressurized cabin (otherwise you´d get one hell of a draft). I´ll try to remember to ask a colleague for confirmation –  yankeekilo Jan 8 at 9:26
    
@Yankeekilo: I remember seeing some documentary where Israeli air force tested it and showed that bird strike at supersonic speed can break fighter canopy (Israel is bottleneck on migratory paths with sea at one side and desert on the other, so they get really huge flocks of birds in spring and autumn). –  Jan Hudec Mar 19 at 21:07

Windows are either made of acrylics (PMMA, brand name e.g. "Plexiglas") or polycarbonate (PC, "Lexan" or "Makrolon") materials.

The small hole is there to provide ventilation and enable removal of moisture/condensation, but the hole is only in the thin protective screen on the inside. The much thicker actual window that holds the pressure is (hopefully) not punctured.

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