Abstract: An additive suited to use in combination with heat transfer media comprises a chemically stabilized nano-particle size powder. Suitable powders include those of copper, beryllium, titanium, nickel, iron, alloys or blends thereof, and carbon. The surface of the powder is modified by surface complexation or physical adsorption with a chemical agent. The additive, when mixed with a heat transfer medium, forms a colloidal dispersion which exhibits enhanced heat transfer capacity and thermal conductivity, stable chemical composition, faster heat transfer rates, dispersion maintenance which are beneficial to most heat transfer systems.