Insulating glazing unit

On August 1, 1865, American engineer and inventor Thomas D. Stetson (1827-1916) filed a patent for an insulating glazing unit. It consisted of two glass panes that were bound together and hermetically sealed at the edges, and dehydrated air between the glass panes was used as insulation.

Utilising dry air was ingenious, since air that contains moisture condenses when it comes in contact with a cold surface; where there is no moisture, there is no condensation. Stetson's invention was before its time, and he never got to see his insulating window panes put into production; they were not manufactured before the 1930s.