A hybrid model of the viscous properties of polymeric matrix blends with isolated (MPBs) and continuous phases (CPBs) was proposed. The hybrid model combines the analytical Hill's model of the average stresses and strains for viscous composites and semi-empirical model of porous materials. A distinctive feature of the model is to calculate the concentration ratios of the average strain rate through the effective volume of the average strain rate. Effective volumes are determined by solving the boundary problem of viscous deformation of the representative volume of two-phase MPBs or CPBs considering a possible porous state of a material. The comparison of the calculation results with the experimental data was made. The new model more accurately describes the viscosity of the two-phase polymer blends than the known phenomenological models. The area of application of the hybrid model is limited to melts of polymer blends, the viscosity of which is inside the Hashin-Shtrikman's bounds. POLYM. ENG. SCI., 59:E212-E218, 2019. (c) 2018 Society of Plastics Engineers