In article FbDPa.36743$H17.10746@sccrnsc02,
Wood Butcher wrote:
It's the latter. A vacuum would be the ideal insulator but
nobody has managed to engineer a window that is strong
enough to keep the panes from flexing inward and touching
and/or breaking.

BZZZT! Vacuum panes exist. 'big' ones. We had 'em for 'sliding glass doors'
opening onto a patio. 4' wide, 6'6" tall. installed in the mid 60's

Art

"Jim Mc Namara" wrote in message
.com...
My understanding is that the dead air space between the panes is either
vacuum sealed or charged with an inert gas. Anybody?

Jum