Improving the fracture resistance of polypropylene (PP) is a major research focus that could pay great dividends for applications. Adding a β-phase nucleating agent, which induces the formation of β-phase spherulites of PP, has been shown to improve the fracture resistance of PP. This is because the parallel lamella stacking, as found in such spherulites, is thought to respond favorably to the shear deformation of the matrix under load. Addition of an elastomer to the mix has been shown to improve the properties further. On page 898 of this issue, Yong Wang and colleagues study the underlying mechanisms responsible for these property improvements. They show that the microstructures can be controlled by adjusting the mass fraction of nucleating agents. Consequently, the mechanical properties of the blends can be easily controlled.