see fig5 a the first insulating layer 301 may be attached not only by electrodeposition but also by means of dip coating using a suspension of inorganic insulating particles however it is difficult to control the thickness of the insulating layer by the dip coating method alone accordingly it is preferable to apply electrodeposition after a thin layer of the inorganic insulating particles has been attached onto the metallic wire by means of dip coating the second insulating layer 302 may be formed by means of dip coating spraying etc using said suspension although the control of the thickness of insulating layer is easier than for the first layer an insulating layer of smooth surface as obtainable by electrodeposition is difficultly obtained the suspension used in said dip coating method etc may be obtained for example by dispersing and suspending inorganic insulating particles in a proportion of 1 3 g to 1 l of a solvent comprising methyl isobutyl ketone as the main component and then adding methylcellulose or nitrocellulose thereto as a binder for the particles the improved life of the inorganically insulated heater of the present invention is attributed first to the fact that in the first insulating layer adhered and formed between the metallic wires of the metallic wire coil the inorganic insulating particles distribute uniformly and no void and other defects develop so that the strength and the electric insulation characteristic of the insulating layer are improved it is further attributed to the fact that the above result influences also on the formation of the second insulating layer leading to uniform particle distribution and formation of uniform insulating layer and resultantly a heater having little of defect throughout the.