the back Board, like 3/16". . the foam & material is about 1/4". (unless someone has put new foam /material OVER the Old) then it could be close to 1/2".
I just bought headliner fabric from Joanne Fabrics for my sunvisor restore. It's 3/16ths and I'm happy with it. About $12 or $14 per yard, and a half yard is plenty for 4 sunvisors.
Joann fabrics, has three different colors of headliner material, make Shure you use headliner spray adhesive only, any other spray adhesive like 3m will cause the foam to melt and bubble, I did mine and it turned out beautiful.
