Go to the sewing store and get a curved needle for upholstery, thread some fishing mono or buy a spool of upholstery thread at the store and go slow and stitch up one side and cross stitch back down the other working the material back together as you go. Try not to pull too hard and leave even space between needle holes.
It works good, lasts several years, and since the material is clear, you don't see it very well unless you are looking for it.
This won't work if the fabric is brittle or just hanging in there.