anyone know if this stuff would reduce heat or noise and not fall off?

I wouldn't use it. They put that in the cavity of the "C" pillar on later model beetles and that was the cause of most of the rust happening in this area.

Yogie

i wouldn't put it anywhere it could trap water, i'm just talking about the area where the coconut hair mats were. the foam itself couldn't be dangerous to metal could it?

It sweats as well and moisture gets trapped against the metal. Water doesn't get in to the C pillar either yet it rusts it away.

Yogie

i see.

what's good, (and won't fall on my head one day) then?

Maybe glue some dynamat to the roof would do it.

Yogie

id go with the dynamat or similar easy to install