No, I do not believe that Dynomat would have any temperature insulating value. Original Dyno mat is rubber with adhesive backing. Extreme Dynomat is tar with an aluminum foil cover. In the heat the tar will quish out and make a mess. Also don't ever plan on removing it.
I lived in Phoenix for 20 years and after seeing what the summer heat does to the tar on the road I would not want it on the ceiling above me.
If you really want heat insulation I would recomend getting a white VX or using regular insulation.
In my opinion Dynomat only reduces rattles.
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