Funny story. My dad was a CPA and worked to dissolve a company that made a revolutionary kind of insulation, an aluminum honeycomb that when stretched formed about a 2 inch thick lattice. So he got all this material and I insulated my parents entire house with it. This was in the 1970's. It is the best insulation I've ever encountered.
One problem though, the house is one big faraday cage. No cell signals, no wifi, 4g, 5g - it's a dead zone.