Diffusion-controlled capillarity phenomena in solids, including sintering and surface profile changes, can be retarded by dispersed particles which are pinned at the surfaces. A model is proposed which predicts that dispersed particles which are more wetted by the substrate material, and subsequently partially imbedded, will tend to have a lower mobility than particles which are less wetted, if the force exerted on the particles by the moving interface is sufficiently low that the particles are dragged by the surface. On the other hand, less wetted immobile particles can provide a greater restraining force than more wetted particles. For a given volume of dispersoid per unit area of substrate, larger particles will provide a greater restraint to interfacial motion. Particle drag at the surface is probably not very effective in retarding sintering brought about by grain-boundary and volume diffusion. Surface diffusion-controlled sintering and surface-shape changes can be strongly retarded by dispersed particles.