The Hansen solubility parameters are typically used, especially in the paint and coatings industry, for selecting suitable solvents for polymer binders. In such applications, the radius of solubility needs to be determined by experiments. Moreover, other calculations, e.g. related to drying of paints, require thermodynamic description over extended concentration ranges. On the other hand, the well-known Flory-Huggins model captures satisfactorily several of the characteristics of polymer solutions, but the interaction parameter of the model usually also has to be determined by experiments. In this work, we present a methodology, based on which the Hansen solubility parameters can be incorporated in the Flory-Huggins model. The resulting model is predictive and yields good predictions of solvent activity coefficients at infinite dilution in several acrylate and acetate polymers. The results are as accurate as other predictive polymer models based on the group-contribution (GC) principle, but in contrast to these models, knowledge of molecular structures is not required in the Hansen/Flory-Huggins model. The new model makes thus use of the extensive literature of Hansen solubility parameters, which are tabulated for very many solvents, pigments and polymers.