The thermal conductivity κ of solid CO2 was studied in the temperature T range of 100–220 K and at pressures up to 200 MPa using the transient hot-wire method. The results are consistent with those expected for a polycrystal composed of small molecules, with κ increasing significantly as the temperature decreases and as pressure and density increase. The variation in κ with temperature is primarily attributed to changes in phonon–phonon scattering and density. The thermal conductivity behaviour is described using a two-basis model, where heat is transported by both phonons and diffuse modes. The density ρ dependence of the thermal conductivity, represented by the Bridgman parameter g = (d ln κ/d ln ρ)T, was found to be g = 6.7 at 190 K, increasing to 9.4 at 110 K as the temperature decreases. This increase is attributed to an enhanced phonon contribution to the total κ.