euromodder,
Again, a reasonable question, but I don't know the answer.
(I never thought we'd be getting this deeply into this.
The product I identified earlier was meant as a general example.
It may in fact be better than what I'm using as it is available in
greater thickness with higher R values.)
Your reasonable information-seeking request deserves a reasoned
information-providing response.
Here's the product from Lowes:
Reflectix Double Reflective Foil Insulation
And here is the manufacturer's website for the product:
Reflectix Inc. - Double Reflective Insulation
Hope this helps.