The properties of the silicone antifoams are reviewed in relation to the known antifoam requirements. Consideration is given to the effect that structural changes have on the performance of the silicone. The storage stability of a silicone antifoam dispersion in lubricating oils is shown to be a function of the antifoam particle size. Mixing techniques involving colloid milling were found to produce antifoam dispersions with the desired particle size distribution. Microscopic examination was found to be a semiquantitative method for determining the quality of a silicone dispersion.