On Mon, 28 Jul 2008 22:56:30 +0100, "dennis@home"
wrote:

There's no need for an insulating air layer to be 6mm thick. That's
one value for a _maximum_ thickness of a stagnation layer in these
circumstances. Layers thinner than this will still have nearly as
much thermal resistance.

They will be proportional.. a 1 mm layer will be 1/6 as good as a 6 mm
layer.

If heat transfer was by conduction, then it would proportional.

However air is a fluid. Heat transfer is predominantly by convection,
not conduction. It's easily mobile, yet very low density. Even at these
dimensions, convection predominates.

A really thin layer will be useless.

We could agree that as a definition of "really" thin. However these
airgaps aren't that thin (unless you squash the foil). A mm or two is
still useful.

tri-iso super 10 is about 30 mm so it is about twice as good as double
glazing, that is, not vey good.

The whole point is that this 30mm is not spent on a single gap, but
rather multiple independent airgaps. That's why they work better.