What is this? Layer under headliner

[Dax]

Finally got into the tear down on my Havasu. It was oh so satisfying to pull out the awful headlines, but there's this thick, ruberry film between the fiberglass and headliner. The side I'm holding in the pic is how it looks like on the fiberglass side.

Does anyone know what this is?
Should I scrape it off?
Should I replace it?
I'll be adding some ensolite for insulation around the whole camper

[Eric Frye]

That is the glue, or more specifically rubber contact cement.