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Solid particles can also act as defoamers according to some of the mechanisms described (e.g. bridging de-wetting mechanism). The filling of defoamer oil with a solid particle can boost the defoaming characteristics to higher levels than that of the individual components [1] [8]. A solid content of only a few percent is sufficient to achieve this. Excessive solid content often causes excessive viscosity of the oil and impairs flow and deformation, resulting in reduced efficiency of the oil. For optimum performance it is necessary for the solid particles to cover the surface of the defoamer droplet. A strong hydrophobic particle will be too compatible with the oil and will be completely wetted by it. If the solid particle is too hydrophilic, there is a risk that it can be removed from the oil droplet into the aqueous phase of the coating. In both cases the efficiency of the defoamer will suffer. The filler has a major influence on the entry barrier and the bridging mechanism of defoamer oil.