Abstract: A thermal mass flow measuring apparatus comprises a sheath having an interior surface and a protective exterior surface. A liquid material having a thermal conductivity greater than about 12 w/(m·° C.) is disposed within the sheath in contact with the interior surface of the sheath. A sensor element, such as a thin-film thermoresistive element or a wire-wound thermoresistive element is at least partially submerged in the liquid material. The liquid material, which is preferably liquid metal, decreases the overall thermal resistance between the outer surface of the sheath and the sensor element.