On "Pelagic Australis" the pilot-house windows are double glazed with a 24mm air-gap. The outer glass is 12mm ballistic stuff (bullet proof) and the inner glass the windscreen stuff that shatters into small cubes. It's been there almost 12 years now without any issues except that we broke the inner on one when taking it out to re-bed it after about 7 years. The bedding is sikaflex 295UV
were made up by a company that does the glazing for bullet-proof limos.
The big front window is about 1.2m by .75m and they have taken a pounding at times from both objects and water
. The worst damage has been done to the corners of one panel by an over enthusiastic painter with a sanding
Double glazing (without a reflective barrier) won't keep radiant heat from the sun out but it certainly keeps the cold out and more or less eliminates condensation
on the glass.