The trends in anharmonicity are balanced by the N2 , which show that the scattering phase spaces are larger for the Sn chalcogenides than the Ge analogues, larger for the selenides than the sulphides, and larger for the Pnma phases than the R3m phases, at least at low frequencies where modes typically contribute most to the κ latt . The longer averaged lifetimes of Pnma GeSe and SnSe compared to the respective sulphides indicate that the larger N2 do not fully compensate for the smaller P. On the other hand, the smaller P of Pnma SnS and SnSe is more than compensated by the larger N2 and results in both Sn chalcogenides having shorter lifetimes than the Ge analogues. For the R3m phases, while GeSe has a larger N2 than GeS this does not compensate for the much larger P in the sulphide, resulting in the selenide having a ∼ 3.2× longer τ CRTA .