Bead Mill for Thermal Interface Material Filler Dispersion: Why Bigger Particles Sometimes Win. Thermal interface materials (TIMs) use thermally conductive fillers — most commonly boron nitride, aluminum oxide, or aluminum nitride — dispersed in a polymer matrix to move heat away from chips and power electronics. Unlike most dispersion applications, published research on boron nitride particle size and thermal conductivity is genuinely mixed: some studies find larger part