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).

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).