ΔL=LαΔT The concept is interesting and applying its formula isn't even tedious, but what are the real factors that determine α here? I understand that thermal expansion is a direct consequence of the average separation between atoms. And that the coefficient can be found through different experiments. But I want to understand why different solids have different coefficients. I think my strongest insight is that α value must be somehow inversely proportional to a solid's density. So we have soft metals like aluminum with high values of α and epoxy with twice that of alumn. And then we have dense metals like steel that don't really expand that much. Titanium is one of the hardest metals I've worked with and its coefficient α is very low. Is there a strong relationship between these two? Or is there a factor more relevant?