fig1 b is a graph showing a disengagement feature of a conventional wet friction material fig2 is a graph showing shear strength of friction material substrates of the wet friction material according to the embodiment of the invention compared to comparative examples fig3 a is a view showing a frame format of an inner structure of conventional friction material substrates fig3 b is a view showing a frame format of an inner structure of friction material substrates according to the embodiment of the invention fig4 is a graph showing a pore diameter distribution of friction material substrates of the wet friction material according to the embodiment of the invention compared to comparative examples first a production method or composing materials that make up friction material substrates of the wet friction material according to preferred embodiments of the invention are described referring to table 1 as shown in table 1 as a composition of friction material substrates of a wet friction material according to the embodiment of the invention it produces friction material substrates making use of four kinds of compositions according to a first example to a fourth example and for comparison it produces another friction material substrates making use of five kinds of compositions according to a first comparative example to a fifth comparative example in composing materials shown in table 1 it uses aramid fiber pulp for a fiber and diatom earth graphite and carbon fiber for filler also it makes use of diatom earth for u201c inorganic filler a b u201d zinc oxide for u201c inorganic filler c u201d barium sulfate for u201c inorganic filler d u201d titanium oxide for u201c inorganic filler e u201d and calcium carbonate for u201c inorganic filler f u201d each at.