I purchased a whole house fan this year and now it is cooler I want to insulate the opening in the attic. I came across these on the internet, but at $90+ I find this preposterous.

I though of just make my own from materials from Home Depot. Is there such as thing as insulation board with an R value of R-40?

https://www.ecomfort.com/QuietCool-W...AaAgXmEALw_wcB