Our previous work showed that, in a cubic pack of solid spheres at low water content, thermal conductivity λ as a function of water content θ behaves as λ(θ) = λ_dry + aθ^b. Here we extend the work to distributions of spheres, showing the effects of water films, contact between spheres of different sizes, and the particle size distribution. We compare our results to measured λ(θ) relationships in soils.