What do you think of 'burled plastic foil', or you could describe it as:
double plastic foil with circular compartments in between, filled with air.
But.. I know what you mean, don't know the specific technical name for it,
but perhaps you will get the right answer as a reaction on this message.
Besides: we had very cold nights with temperatures to -9 degrees C.
I protected the cold frames with a three thick layer of 'noppenfolie' and I
hope the plants are still smiling at me when I open the frames after this
period of frost!
Pells are still flowering in the (heated) glasshouse by temperatures of 7
degrees C above zero.