Our screens are manufactured from a specialist 9 layer quilted fabric:

 light grey inner face. 

3 layers of 1.5mm foamy fabric, 

3 layers of metallic film, 

1 layer of polyester fibre & 

1 outer layer of strong metallic silver fabric.

Here's what it looks like inside: (foil outer surface is on the top, grey fabric surface at the bottom of this first picture)

The fabric is excellent at providing heat and cold insulation, but just as importantly it holds its shape properly when it is vertical on your windows. Several other versions of these things are made of softer / more flexible quilting which just ends up sagging through the night to leave cold gaps on your windows.