Thermal conductivity measurement methods are divided into steady-state and transient approaches, each with different principles. In the thermal silicone industry, a common method is steady-state heat flow testing based on ASTM D5470.

ASTM D5470: thermal transmission testing of thin, thermally conductive, electrically insulating solid materials

In the steady-state heat flow method, a specimen of known thickness is placed between two plates under controlled heat flow and pressure. Heat flow, specimen thickness, and the temperature gradient between the hot and cold plates are measured. Thermal resistance values at different thicknesses are fitted to a straight line to obtain thermal conductivity. The method has the following advantages and limitations:

1. Measures both thermal resistance and thermal conductivity.

2. Well suited to simulating actual operating conditions, but imposes specimen-thickness requirements.

3. Contact thermal resistance affects the results.

4. Reaching steady state requires longer test times. Steady-state heat flow test diagram: