Solubility diagrams of a series of carboxylic acids in a matrix of linear polystyrene have been measured using a gravimetric method on samples immersed in solvent, as reported earlier [Bernardo G, Vesely D. Eur Polym J 2007;43:938–48]. The results show that the amount of solvent, swelling the polymer, reaches an equilibrium saturation which has a unique and reproducible value for each system and temperature. An analysis based on Flory–Huggins theory shows that all data presented here can be well interpreted with an interaction parameter in a simple form: χ=a+(b/T). An excellent fit can also be obtained using the van’t Hoff equation. An analysis based on total and partial (Hansen) solubility parameters has also been investigated.