Abstract: In a wet friction material, inorganic filler of small particle size is added to fill clearances or space between fibers with the inorganic filler. The inorganic filler is attached to the fibers with each other to reinforce strength of the wet friction material when an impregnated resin is hardened. Absolute specific gravity of the inorganic filler is set at a fixed value so as to make its compounding quantity small, thereby assuring a pore diameter of a friction material substrate without filling pores of the friction material substrate with the inorganic filler.

Abstract: In a wet friction material, to be able to reduce a drag torque, while being greater in a disengagement feature and a positive ?-V slope characteristic by keeping a pore diameter large without generating strength reduction or increase in settling quantity. By adding small-particle inorganic filler 2, it attaches the inorganic filler 2 to inter-fiber 3 and it can obtain an effect to improve strength of friction material substrates 1 by connecting the inter-fiber 3 when an impregnated resin is hardened. Moreover, by keeping an absolute specific gravity of the inorganic filler 2, its compounded capacity becomes small and it can secure a pore diameter 5 of the friction material substrates 1 without being filled in pores of the friction material substrates 1 with the inorganic filler 2. As a result, it makes faster to absorb ATF from a friction surface. Therefore, it improves the disengagement feature and the positive ?-V slope characteristic, while reducing the drag torque.