There are basically two kinds of bamboo shakuhachi these days - natural bore called Jinashi and JI filled bore called Jiari .
Ji is a paste made of a mixture of Japanese urushi lacquer and tonoko powder. The result is a Plaster of Paris-like paste that is carefully hand applied to the inside of the bore to manipulate the resonance spots.
My shakuhachi are mostly jinashi (my chikusing style) because I like the more natural bamboo timbres, but a good shakuhachi requires at least some addition and subtraction from the bore so that the flute will play with more dynamic response. This is a time consuming process and this is why full Jiari shakuhachi cost thousands of dollars.