This type of defoamer usually uses polydimethylsiloxane with low surface tension, which is widely used in defoaming in lubricating oil (such as motor oil, transmission oil), oil production, refining and cracking hydrocarbon heavy oil.

Low viscosity methyl silicone oil is easy to disperse due to its small surface tension, thus effectively defoaming, but its solubility is high, which affects its sustainability. Relatively speaking, high viscosity silicone oil (above 1000mm2/s) has weaker defoaming ability and low solubility, so it has better durability. Mixing silicone oils of different viscosities can balance the defoaming and anti-foaming effects. The general rule is to use high viscosity silicone oil in low viscosity foaming liquid, and vice versa.

The most commonly used methyl silicone oil viscosity range is 100-100000mm2/s.

In addition to polydimethylsiloxane, other types of silicone defoamers are also used in specific occasions. For example, polymethylphenylsiloxane is suitable for ethanol defoaming; polysiloxane containing ethyl or propyl is suitable for coating and ink defoaming.

Although the surface tension of fluorinated silicone oil is higher than that of methyl silicone oil, its solubility in hydrocarbon compounds is lower, so it is often used for defoaming in non-aqueous systems.