I have done many headliners, and I always use the same formula and have had 100% success.
Any crafts store or cloth store (Jo Ann Fabrics, Crafts & Stuff, ect) sells automotive headliners in many colors. Get about 2 more feet than you need, measuring front to back. Go to your local home improvement store and go to the paint/adhievese section. Buy a can of 3M Super 90 spray adhesive. It is like $16 a can but it is the ONLY spray you should use. 3M also makes Super 77 for headliners, but it does NOT hold up to high temp/high humidity areas.
Remove your headliner board, peel off the headliner and scrape off ALL of the remaining foam. Most of it will come off with the wide end of a vacuum using the tube attachment, a Shop Vac works great. Use a wire brush or hard bristle brush to remove any remaining foam. Make sure your headliner board is as clean as you can get it.
Lay out the headliner board in a dry, well ventilated area being sure to cover the floor with paper, extending the paper about a foot out around the headliner board, being sure to have paper under all the holes in the board such as the dome light. Lay out your new material over the headliner board, centering the material over the board. Now fold the material back half way, so the front half of the headliner board is exposed, and the half of the material that will be covering that half of the board is now folded back onto the back half, with the foam side up. Do NOT crease the material, just fold it over.
Now spray the Super 90 all over the headliner board going both side to side and up and down, give it a solid coat, covering 100% of the headliner. Do the exact same on the back side of the material that will be covering that half of the board. Let it sit for 10 to 15 minutes. After letting it sit for 10 to 15 minutes, carefully start folding the material back over the glued half of the board, starting to attach it to the board from the fold point. Use light pressure on the material as you gently lay it and smooth it out. I like to use a piece of news paper to help my hand glide over the material.
Once that is smoothed all out, fold back the unglued half and repeat. Once everything is smoothed out, allow it to sit for at least a half an hour. Using a razor blade, cut out all the holes in the headliner and trim off the access around the edges. You will need a few razor blades as the access glue tends to gum up the razor.
Put it back in your car.
This method has worked great in South Florida summers for a long time, the longest going on 6 years with no drooping.
