A solvent-free resin mixture which is curable by thermosetting, in particular for use as a highly heat-resistant impregnating, varnishing and casting resin for the insulation of electrical conductors and windings in electrical machinery and equipment, contains at least one reactive liquid epoxide compound, at least one reactive liquid polyisocyanate and at least one latent hardener for these components; the mixture also contains triallyl cyanurate as a crosslinking agent.