any of a diverse class of chemical polymers manufactured in the form of fluids, resins, or elastomers. Although they are partially organic in composition, the molecules of silicones differ from those of most polymers in that the backbone of their structure does not contain carbon, the characteristic element of organic compounds, but is a polysiloxane chain, in which atoms of silicon and oxygen alternate. In most members of the class, two organic groups, usually methyl (−CH₃) or phenyl (−C₆H₅), are attached to each silicon atom.

Silicone fluids are exceptionally stable to decomposition by heat, water, or oxidizing agents and are good electrical insulators. They are used as components of hydraulic fluids and emulsion-breaking compositions and to impart water-repellency to textiles, paper, and many other substances.

Silicone rubbers are valued for their electrical insulating properties, chemical stability, and the wide temperature range over which they retain resiliency. Silicone resins are used in protective coatings and electrically insulating varnishes and for laminating glass cloth. In the second half of the 20th century, silicone gels were used as breast (mammary gland) implants in women, though this application was curtailed in the early 1990s owing to its possible health risks.