YouTube / Air Zoo
The SR-71’s windows might look like regular old glass to an average person, but they’re much more complicated than that.
The “glass” comprises layers of various thicknesses of glass, quartz, and silicon, with some air gaps between the glasses, so it doesn’t fog up.
Its windows are specially made because they are subject to tremendous amounts of force. When a Blackbird reaches three times the speed of sound, the windows can reach up to 420° Fahrenheit.
Inside the cockpit is a different story, however, as it was a pleasant and comfortable 80° F.
Interestingly, the insides of the windows could also heat up, allowing pilots to warm up their tube lunches by pressing them against the windows. That’s pretty neat!