Abstract: An inorganic fibrous insulating material is provided that exhibits an excellent insulating performance wherein heat transfer by air convection within the insulating material and by the inorganic fibers is suppressed. This is an inorganic fibrous insulating material in which a plurality of inorganic fibrous mats are stacked. The inorganic fiber constituting the inorganic fibrous mat has a fiber diameter of 3 to 5 ?m and a fiber length of at least 20 mm. The inorganic fibers are bonded to each other at their contact points by a thermosetting binder. The areal weight of each inorganic fibrous mat is 300 to 600 g/m2, and the orientation angle of the inorganic fibrous mats with respect to a direction perpendicular to the thickness direction of the inorganic fibrous insulating material is inclined at from more than 0° to not more than 20°.