Thanks for all the input. Blocking hacker RF/EM signals or other espionage is certainly not my concern on this project.
My question about material is directed at selecting the proper type of fabric (nylon, polyester), I guess ... mainly concerning which would maintain proper thickness and longevity of the wallet.
I guess I've decided in my head to not trim the top of the divider with leather, but instead sew a hemmed edge with whichever fabric I choose. I sew all leather by hand, but I do have an old Singer I use to hem pants and such, so it wouldn't be too intimidating to tackle this with that technique.
Again, thanks the input! Maybe I'll report back with pics, etc if it would help the next person.
Is there another term for this material? When I google "chevre" all I get back is goat cheese. Which was distracting, because that stuff is delicious!