Insulation, Peel n seal and other budget insulation ideas
Oh, before I found the Noico stuff I also bought a few packs of this Zirgo UltraMat.
UltraMat Heat and Sound Barrier Sheets | johnnylawmotors.com
I used it to do the roof because it is crazy light weight. It isn't a peel-and-stick. Used some 3M spray adhesive and then some aluminum tape I got at Lowes/Home Depot.
I decided not to use it on the floors because it felt too light (very little sound deadening). But the heat difference was HUGE. The car went from being an oven to comfortably warm on a 90+ sunny day.