Hey Craig ...
In an effort to not get near the line that defines "promotions of products/services", I'll keep this brief. If you, or anyone else, are interested in more detail, please feel free to pm me.
The stuff that Overton's was selling was "The Insulator" and was specifically branded as "thermal-acousitc insulation". I was able to purchase a packaged 4'x6' sheet (forgot which of the two thickness I purchased) from a local RV store out of their product/supplier catalog.
I'm fairly certain the stuff is Manufactured in AZ by a company somewhere near Chandler.
Hope that helps ...
Btw, speaking from experience ... DO NOT store/leave the shipped package with the blue ink on your upholstery if you don't get to the project after you order this product. Mine bleed onto the upholstery and dyed the white into a blue in some spots. I couldn't, nor could any of the professionals, get the ink out, and we had to redye/paint the seats with a color matched white.
Good luck with your project and go safely enjoy the water!