Polymers with silicone backbones. These might be delivered as an oil- or a water-based emulsion. The silicone compound consists of an hydrophobic silica dispersed in a silicone oil. Emulsifiers are added to ensure that the silicone spreads fast and well in the foaming medium. The silicone compound might also contain silicone glycols and other modified silicone fluids. These are also heavy duty defoamers and are good at both knocking down surface foam and releasing entrained air. Silicone based defoamers are also suitable in non-aqueous foaming systems like crude oil and oil refining.