Yes, I doubt it is fiber, let's see...

Fuji does quite a bit of paper. There used to be even more, but you all know the state of things at the moment.

http://fujifilm.jp/personal/film/monochrome/paper.html

I think Rembrant V is the only fibre paper they make and it is multigrade. For graded fibre paper made in Japan I believe Oriental is the only choice.