Yes, the average length of the fibres in Japanese kozo (mulberry) paper is around 6mm which makes the paper very strong. Trying to tear across the fibre alignment, for example, is quite difficult in the heavier papers. Kozo paper is so strong that traditionally it was made into articles of clothing. Mulberry is the most common fibre used in traditional Japanese paper but there are others - hemp is one (and possibly the oldest) and it's certainly the strongest fibre used in Far Eastern paper. Another common fibre used in China is that obtained from bamboo; the fibre length is very short however and therefore the paper is not very strong - good for calligraphy though, and a very renewable source as a single bamboo can reach its full height (30 foot) in one year.

There are quite a few places now selling conservation-grade Far Eastern papers in this country; I haven't jet checked yet if takuhon inks and pads are available though.