The outer pane of an aircraft window is 0.47 in ( 12 mm ) thick and the inner pane is 0.16 in ( 4 mm ) thick. They are separated by a 0.23 in ( 6 mm ) air chamber, making a total thickness of 0.87 in ( 22 mm ) for the entire window, which may seem thin, but the outer pane is thicker than the plane's fuselage.