On 26 Jul, 20:12, "dennis@home" wrote:

A piece of cling film with a 25 mm air gap either side would be as good.
Its the air supplying the insulation not the foil.

You haven't seen the insulating foils, have you?

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.