I pulled out 1"+ thick fiberglass insulation when I removed it. Is there something specific I install or can I just use one of the newer thin car insulation/sound blockers. The headliner doesn't get attached or glued to it (does it?), just to the bows and glued around the edges. I couldn't tell with the condition of my other one. The insulation was glued in and there was glue across the support bar like the headliner may have been glued.

 

I went to Home despot and bought the smallest roll of home fiberglass insulation and cut the thick part in two,, and contact cemeted it to the roof,, it helped take out the wrinkels and sags

 

I don't know for sure since I haven't gotten that far or researched it. I think I saw something about removing the wrinkles, sags and custom fit the installation by using a heat gun on low on the loose fitting areas to shrink the headliner once it is completely installed and securely glued on all edges.
I think it was on one of the auto restoration shows a while back, so I don't know if it works for ours or what type of material to do it with. It tightened all the loose areas and put tension against the bows and contact points to give it a custom fit. Maybe someone else would know more about it?
I wish I hadn't thrown out my old one, I would have liked to have tested it. It makes sense to me, but I wouldn't want to damage a new one trying it out!

 

You could always order the replacement insulation from NPD or any of the other vendors. Use spray adhesive to glue the insulation to the panel. I applied some sound dampening (Second Skin) to the metal then the insulation to that. The headliner gets glued at the front and rear windows and the windlace secures it to the body along the sides.