Headliner Insulation - undercoat?

I have given this a lot of thought for my own car when the time comes, and I think straight up non foil backed fiberglass home insulation is what I'm going to use.
It's light enough to to be held up with contact cement and will def do the job.
(For a carboard liner, but you probably have a cloth liner) and I don't think I would try it with that.

Noisey as hell when it rains isn't it? :-)