It is calculated that the thermal conductivity of pine boards is 3.7 times that of pine sawdust. How to explain this difference?

The fact that a pine board is a monolithic piece of wood in which molecules interact with each other throughout the volume of the board and are inextricably linked with each other. Therefore, the heat is transferred better.

And pine sawdust, when put together, are small pieces of wood that are loosely connected to each other, with air gaps, so the molecular interaction is much worse in sawdust than in pine. Therefore, thermal conductivity as the rate of interaction of molecules is much lower.