A detailed model describing particle growth and morphology in polyolefins synthesized using supported metallocene catalysts is presented. The multigrain model (MGM) is extended to consider metal extraction and the effects of polymer particle compressibility, in addition to monomer sorption and mass and heat transfer considerations. The effects of active metal extraction into the polymer phase and the pores of the particle on the kinetics of polymerization and morphological features of the polymer particle are studied. The effects of greater compressibility of polymer particles on morphological features such as particle porosity are studied. Model predictions for porosity and morphology are shown to reproduce similar trends as have been reported in experimental studies.