The present invention discloses the use of a supercritical fluid to improve the homogeneity of heterogeneous bi- or multi-modal resins resulting from a physical or a chemical blend of two or more fractions of the same type of polymer resin, said fractions having different molecular weights or of two or more polymer resins having different chemical compositions, or both. It also discloses the use of a supercritical fluid to improve the dispersion of additives or fillers into a polymer resin. It further discloses the process for preparing the homogeneous resin.