Question about headliners (original types)

[OregonNed]

I have a question about factory style headliners and thought I'd ask here since I did not have one to examine in my '68. I know the ones I see for sale are vinyl covered and padded with what I would guess is a thin layer of foam. What is the base material of the headliner itself? Is is a thick cardboard, or other material? I am guessing that is is slightly concave to fit into the ceiling of the cab. In any event, the wheels are turning again in my head for customizing one, and thought the best approach was to deconstruct the cover of one for my idea, using the base material - perhaps a used one that didn't have to be in the best of shape. Thank you