We present a detailed small-angle neutron scattering investigation of mixtures of poly(ethylene oxide) (PEO)/polyhedral oligomeric silsesquioxane (POSS) hybrids, a popular nanofiller, addressing the conformation of the model-grafted nanoparticles as well as their influence on the linear polymer matrix in which they are embedded. The nanofiller has a well-defined graft arm length and is monomolecular. Because of the identical chemical nature of the grafted arm and matrix chains, it can be considered as an ideal athermal mixture. We have introduced a random phase approximation approach with general application possibilities for-Other grafted nanofillers, combining the star-like and particle-like characteristics of the POSS nanofiller. The size of the nanofiller remained unaffected and Gaussian upon mixing with linear Chains of various lengths, and no aggregation of the nanofiller was observed. This turns the POSS-based nanocomposite into an interesting model compound. The mixtures of PEO chains with the octafunctional PEO-POSS nanofiller were found to resemble those of a Micellar system whereas within experimental uncertainty the radius of gyration of the embedding matrix remained basically unaltered despite some tendency toward shrinking.