A heat-transfer material is produced by: preparing a body of metal serving as a cathode; subsequently keeping a surface of the body and an anode in contact with a plating aqueous solution; and applying a direct electrical potential between the anode and the cathode to cause a plating current to flow through the plating solution to produce slime from the anode and to lay deposits of plating metal on the surface of the body and moving the slime to the surface of the body to lay deposits of the slime on the surface of the body, so that the deposits of plating metal and the deposits of the slime jointly form on the surface of the body a porous layer which has minuscule projections of electrodeposits densely formed on one surface of the layer directed away from the body.