Originally Posted by AGWhitehouse
The industry "Energy Star" efficiency windows right now are R-5 (U-0.20).
Now the OP is really going to be confused. His location is England. U value in Europe is measured in Watts......., and in the US they are measured in BTU........ (too many units to list them all).
So they are different. I read where European U value is 5.678 times bigger than US U value. If this is accurate than a US 0.2 equals a European 1.14 U value. These guys were advertising 1.2. So That would make these rather good windows, but not extraordinary windows.