closely aligns with the experimental value (1.0 W m -1 K -1 ) and is also comparable to that of other layered thermoelectric materials, such as BiCuOSe (1.0 W m -1 K -1 ) and Bi2O2Se (1.1 W m -1 K -1 ). Importantly, the lattice thermal conductivity is highly anisotropic in both Sb2Si2Te6 and Sc2Si2Te6, resulting in average κx,y/κz ratios of 1.82 and 2.24, respectively, at 300 K. The anisotropic nature of lattice thermal conductivity can be attributed to the difference between relatively weak (van der Waals) interlayer interactions along the cross-plane direction and strong (covalent) intralayer interactions along the in-plane direction. Further analysis of the atomistic origins of thermal transport behaviour in these layered compounds was performed by querying the frequency-dependent phonon group velocities, lifetimes and cumulative lattice thermal conductivity, as provided in the Supplementary Information (Figures and).