In the diagram there you can see we’ve inserted Heat sink, perhaps the gap pad or gap filler, or even a thermally conductive Heat Pipe. And you measure the temperature difference across that gap, you're trying to remove, and then take into account the area of material and the thickness of that gap to measure the heat flow in the formula. Now these two substrates, the heat source and cooling plate are not necessarily smooth. And it’s that form-fitting and how well the material stills in and renews air pockets that increases the performance and reliability of the device by having the best thermally conducted solution.
An example of removing the air could be by filling that with a soft shore double zero-gap pad Fin heat sink, shore rating of five to 15, to renew and fill those air pockets. Softer thermal interface materials have that gap feeling property inability to have the most efficient movement of that heat within the device.
