Abstract <p>The methods of optimizing the technological properties of an electrically insulating heat-resistant varnish based on polymethyl phenyl siloxane resin and acrylic copolymers are considered. It has been found that a rise in the proportion of acrylic film-forming agents in polymethyl phenyl siloxane resin accelerates the drying of varnish compounds and makes them less dense and more viscous. The addition of methyl methacrylate and butyl methacrylate copolymers into polymethyl phenyl siloxane resin increases the average molecular weight of the varnish compounds, makes the coating less elastic, and decreases its strength and hardness. It is shown that coatings obtained using Degalan LP 65/12 and Dacryl SP 652 as film-forming copolymers exhibit the lowest brittleness. As a result, the physical modification of polymethyl phenyl siloxane resin with high-molecular acrylic copolymers improves the physical and mechanical, and strain-and-strength properties of this resin.</p>