In this vein, we have proposed various analyses that can be used to gain better insight into how fillers atoms suppress the thermal transport. Of particular note are the constant relaxation-time model to quantitatively attribute changes in 𝜅 latt to changes in the phonon mode group velocities and lifetimes, and the approximate model for phonon linewidths to attribute changes in lifetimes to changes in the phonon-phonon interaction strengths and the numbers of scattering pathways. These tools may prove useful both to better understand and to compare the impact of filler atoms on the heat transport in skutterudites and other cage compounds.