"Andy Dingley" wrote in message
...
On 28 Jul, 12:09, "dennis@home" wrote:

They're not a single layer, they're a quilted blanket that contains
_multiple_ airgaps. That's why they have better performance than a
single layer of clingfilm.

Only if they trap a significant amount of air, the ones I have seen
don't!

They trap an _insignificant_ amount of air, that's their virtue
(Assuming that "significant" is taken to mean "larger" than
"insignificant", for the purpose of our discussions here).

So there is no air to provide insulation then?
I will give you a hint.. it isn't the mineral wool in mineral wool that
insulates, it isn't the cellulose in cellulose fibre that insulates it isn't
the plastic in polyurethane foam that insulates and as you say there is an
insignificant amount of air in foil insulations.


Because they only trap small individual volumes, the temperature
differences across the volume is too low (relative to the space) to
set up an efficient convection cell. This is why they're more
efficient that clingfilm (and a large convective cell) and why they
need multiple layers (to reduce temperature differences across each
cell).

You get a static layer of air about 6 mm deep on any surface.
You don't need to create cells to make it work.
Cling film will have about 6 mm of static insulating air on each side just
like double glazing does.
Foils aren't thick enough to have this 6 mm layer of air so they conduct
more heat.
You have a basic problem with your physics ATM.