Porous hollow silica particles (HSPs) are presented as new templates to control the product morphology in metallocene-catalyzed olefin polymerization. By selectively immobilizing catalysts inside the micrometer-sized porous hollow silica particles, the high hydraulic forces resulting from polymer growth within the confined geometries of the HSPs cause its supporting shell to break up from the inside. As the shape of the support is replicated during olefin polymerization, perfectly spherical product particles with very narrow size distribution can be achieved by using HSPs exhibiting a monomodal size distribution. Furthermore, the size of the obtained product particles can be controlled not only by the polymerization time but also by the size of the support material.