We explore the effects of adding silica particles to blends of two immiscible polymers, polyisobutylene (PIB) and polyethylene oxide (PEO) across a wide range of compositions, and particle loadings of up to 30 vol %. The silica particles have strong affinity for PEO, and hence, if there is sufficient PEO to fully engulf the particles, a combined phase of particles-in-PEO is formed. We construct a composition morphology map which reveals two microstructures that are qualitatively different from those seen in particle-free polymer blends: one in which particles are bonded together by small menisci of PEO, and the other in which a highly-filled particles-in-PEO phase percolates throughout the sample. Particles widen the composition range over which co-continuous structures appear. Overall we find that particles affect the morphology greatly when the polymer preferred by the particles (PEO) is in a minority, but only modestly when the preferred polymer is in a majority. (C) 2017 Elsevier Ltd. All rights reserved.