The headliner is made from a thin knit fabric bonded to a layer of polyfoam which is glued to a hard shell. Over the years, the foam deteriorates and the fabric drops away from the shell. You cannot reattach the fabric because the foam will no longer hold it. You must remove all the old fabric, scrape off all the remaining foam and glue a new piece of headliner fabric to the hard shell beneath. Headliner fabric can be found at large fabric shops like Jo-Ann Fabrics, or from auto upholstery shops.