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Active ingredients with various chemical compositions are suitable for formulating defoamers. The effectiveness of the defoamer is always dependent on its partial incompatibility in the application medium. This permits formation of defoamer droplets in the system, without causing film or surface defects due to excessive incompatibility. Defoaming is thus always a compromise between efficiency and compatibility. At the same time, a high defoaming power is required. The mostly commonly used defoamer active ingredients are described below. In practice, combinations of active ingredients are used to formulate very powerful defoamers.