Abstract: A method of insulating an electrical conductor by applying thereto a coating of a polyesterimide resin which can be hardened through its free OH groups from a resin melt at above 100.degree. C., wherein the resin used is solvent-free and has been prepared by esterification or ester-exchange of starting materials for the polyesterimide in the presence of an excess of one or more short-chain diols and subsequent removal of the diol or diols in such a way that the condensation is only effected to an extent such that the Durrans softening point of the unhardened resin is not above 150.degree. C. (preferably not above 100.degree. C.) and the viscosity of the molten resin at 180.degree. C. is not above 5000 (preferably not above 1000) mPa s (cP). This process avoids the disadvantages encountered when a solvent is present in the insulating bath.