A model is proposed for thermodiffusiophoresis of droplets growing in a ternary gaseous mixture. The model is compared with experimental data on thermodiffusiophoresis of dioctyl-phthalate (DOF) droplets generated by homogeneous nucleation in an upward thermal diffusion cloud chamber containing different gaseous mixtures of DOP vapour with helium and argon. At higher pressures in the chamber, a reasonable agreement of experiment with theory is found. At lower pressures and higher concentrations of helium, the model predicts a stronger influence of thermodiffusiophoretic effects than is observed.