A thermodynamic model is developed to investigate the extent to which a free polymer, B, can be solubilized into a thin shell layer of grafted A chains of core-shell impact modifier particles. When there is a favourable enthalpy of mixing, free chains of A and B are fully miscible. However, when the A chains are grafted to a surface, only limited amounts of B can be solubilized into this grafted shell due to the conformational constraints. The model assumes a planar shell that only swells in one dimension and ignores any interfacial effects. While enthalpic and entropic terms in the free energy expression favour solubilization, conformational changes for both the free B chains and grafted A chains oppose solubilization. The extent of equilibrium solubilization of B in the shell of A, (phi(B))(s), results from balancing these competing effects. Significant levels of solubilization can occur if the interaction energy between A and B is sufficiently favourable. How favourable the interaction must be depends on the molecular weights of A and B and the initial shell thickness. In general, the model predicts that solubilization is favoured when the B chains are small and the A chains are large and initially exist in a thin shell layer.