Roman,
I'm using the mylar with the bubble wrap inside right now. Definite has insulating qualities, but I'm not quite sure how effective it would act as a 'heat shield'.
Never heard of diamond pressed mylar, but found out this after a quick search,
"- Diamond pressed for increased light diffusion and easier handling
- 50% more reflective than standard black & white sheeting
- Flame Retardant with Total Blackout
- EMP Guard"
Also seems to be about 4 to 5 times the cost of good ol' mylar.
Hope this helps!
Hope this helps!