A new mathematical model describing the build-up and relaxation of elastic tensions inside growing particles during the heterogeneous polymerization of olefins is described. Mass transfer resistance can lead to spatial variation in the expansion rate of polymer which creates tension. This can cause the particle to break up. The reciprocal interaction between morphology and mass transfer resistance is examined by applying the model to two cases where experimental data is available. It was found that the model predicts the formation of hollow particles in the presence of severe mass transfer limitations, in accordance to what is found experimentally. Model results predict that rupturing occurs early in the course of polymerization when monomer concentration gradients are at a maximum inside the growing particles.