On my 66 SS,I purchased the complete kit w/insulation from OPG.The white insulation is 3/4 thick and fairly soft.I have fitted the bows in the car with no headliner to check clearance for insulation and it seems too tight.
The question is ;has anyone tried using this insulation or have any opinions about it.I like the idea to make it quieter and cooler but I'm afraid it will may the headliner puffy looking

I put what sounds like the same white insulation in my 67 but it came from NPD.
No problems.
Glued it to the roof, after putting POR15 on the roof, with 3M spray adhesive.

The factory tar based insulation is still OK and in place...maybe 1/8 " thick?
If you are happy wth the look , I may try it.

Herbie , I may have PM'ed you about sail panel install methods ...any hints ?