<p>A rheological model was developed to predict the aging behavior, i.e., the increase of viscosity over time, for plastisols containing a fraction of plasticized processed PVC. The model is valid for low-concentration plastisols, composed of a bimodal virgin resin and a monomodal processed PVC powder which is initially plasticized with at least 33 wt% of diisononyl phthalate (DINP). The swelling rate was determined for individual spherical particles of each type and accounts for variations of the transfer surface during diffusion of DINP. The viscosity of this multimodal suspension was subsequently determined according to the Farris approach (Trans Soc Rheol 12:281–301, <CitationRef CitationID="CR7">1968</CitationRef>). Predictions of the model are congruent with experimental data and a subsequent variational study aimed at completing these observations by investigating the effects of parameters that cannot be varied experimentally. Results demonstrate that the aging phenomenon depends on several factors such as amount and initial plasticizer concentration of processed PVC but also initial radius and size distribution as well as shape and deformability of particles. Limitations of the model are also discussed.</p> Graphical abstract <p></p>