New foam should be there to keep the glue from saturating the fabric and showing thru. You can carefully replace the fabric only, with good glue and careful application. But I wouldn't expect good results on your first try. I'm guessing here, but If you used a good marine vinyl (because its thicker, and has its own backing) you may not need the foam backing. I got a replacement headliner from gulf fabrics in Tampa it has new foam backing. There's no pricing info on their site, but a phone call would provide that info. Also, try the search bar, I know folks on here have replaced their liners, some are customized.