Why not use a product designed for the application,

https://www.summitracing.com/search/part-type/heat-barrier-and-sound-deadening-mats

Yes it works, the size of each piece is large yet small enough to be manageable, on my 46 did my cab interior including firewall, floors, behind seat, behind door panels and a little left over.

Chuck


Hank: 46 Chev 1/2ton shortbed
2023 Miata RF Club