a method of manufacturing an air permeable electrocast shell comprising forming a conductive layer on the surface of a model , placing a layer of elutable particles into close contact with the surface of the conductive layer and effecting an electrocasting treatment to deposit metal between the conductive layer and the particles , except for the points of contact between the conductive layer and the particles , and between adjoining particles . the deposit of the metal is controlled so that the thickness of the electrocast shell is less than that of the particle layer . thereafter , the particles are eluted from the electrocast shell to form innumberable fine vent holes which open at both surfaces of the electrocast shell .