In Fibers class we made both Western-type paper (where you chop up the
material, such as in a blender), and Japanese-type paper. The strength of
the Western paper is from the number of short fibers, hence a thicker paper.
In Japanese paper, the plant fibers are not chopped up. Rather, they (as
was mentioned in previous replies) are cooked in soda ash and then pounded
so the fibers separate. The strength of this paper is in the length of the
fibers, which interlock. Beautiful "rice" paper has long visible strands of
fibers clearly visible through the thin sheets. The process in making
Japanese paper is quite long, and the chances of tearing the wet paper is
quite high. Kozo and Gampi are two fibers that are commonly used in Japan.
When I made Japanese paper, I mixed one of these with fibers harvested
around my house; corn stalks, cat tails, and even burdock stems!