Hello! I'm writing an essay on 'relationship between density and thermal conductivity'. Could anyone explain to me the relationship? e.g. is it proportional or reciprocal? I'm kind of closing to the answer by doing an experiment. I took two concrete blocks with different densities and got the thermal conductivities. The answer I got is 'denser concrete has higher thermal conductivity'. But the real questions is, can I generalize this statement? If I can, could you give me some details why I can do so. I heard that this is applied for every material in the universe, but I'm not sure. Thank you!