The crystal sizes and melting points of polyethyleneoxide, crystallized in the presence of silica nanoparticles, are only affected for particle loadings larger than 20 wt %. X-ray scattering shows that the distribution of particle spacings in the semicrystalline state is always significantly broader than in the melt, even though the mean particle spacing is unchanged. We thus conclude that. at low loadings, the polymer "forces" the nanoparticle "defects" out of their way to crystallize in a minimally perturbed form. For higher loadings, the crystals become smaller in response to increased particle induced confinement. In contrast to currently held views that the particles control the crystallization process, e.g., by providing heterogeneous nucleation sites, we Find that the crystalline lamellae dominate; i.e., they manipulate the nanoparticle dispersion, especially at low loadings.