With the chemically-inert noble gas fillers, the effect of filling on the heat transport is effectively separated from any impact from the reduction or oxidation of the host framework that may occur with other filler chemistries. This makes these filled skutterudites an ideal "toy model" for exploring how the size and mass of filler atoms and their interaction with the host framework affect the thermal transport. However, we note that we would not expect these materials to be viable thermoelectrics for (at least) three reasons: (1) it would likely be impractical to introduce volatile inert gases such as these into CoSb3, and to then retain them under the large temperature gradients across working thermoelectric devices; (2) the heavier noble gases, which have the largest impact on the 𝜅 latt , are both rare and expensive; and (3) considerably larger reductions in 𝜅 latt have been demonstrated with other fillers.