Characterizing a material in powder form presents many different challenges and considerations than the same material as a rigid body. Particularly, powders are much more susceptible to environmental changes due to their small size and lack of strong connection between particles. Therefore, it is often much more useful to measure the effective thermal conductivity of a powder, which considers the conditions of the surroundings as a whole. For example, since powders are loosely packed, there is air present throughout the sample. The amount of air present will change depending on the compressive load placed upon the powder; a higher force will result in a tighter powder-packing, and thus less air. Measuring the effective thermal conductivity takes this into account, which is important as the sample can be arranged to best represent end-use conditions.
