In article , Nick Maclaren
writes

The glass is 1/2" cavity K glass. Definitely worth it. Condensation
is minimal and little heating is needed. It won't save money, but you
shouldn't lose money over its lifetime.

I'm curious about this one. When double glazing first came out, I was
told that the thinner the gap the better the thermal insulation, as
convection would not be so rapid in a narrower gap. A wider gap was
required for noise insulation, ideally with a tapering section so there
were no resonances. Now DG firms seem to be plugging wide gaps. Is this
because profit margins are higher on chunkier frames, or have the laws
of physics changed in the last twenty years?

Jon
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Jon Rouse