In 1930, the American engineer C.D. Haven developed an insulating windowpane. Patented in 1938, the windowpane was called ”Thermopane”.
The layers of glass were held apart by metal spacer bars that were lead-welded to the glass. The space between them was filled with dehydrated air. In 1941, the insulating window unit was registered as a brand name of the Libbey-Owens-Ford Glass Company. The "thermopane" became popular in the 1950s and '60s. In Europe, the windowpanes were manufactured in Belgium.