Silicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber

Elastomer

An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...

-like, they are used in sealant

Sealant

A sealant may be viscous material that has little or no flow characteristics and stay where they are applied or thin and runny so as to allow it to penetrate the substrate by means of capillary reaction...

s, adhesive

Adhesive

An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...

s, lubricant

Lubricant

A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat...

s, medical applications

Medicine

Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

 (e.g., breast implants), cookware, and insulation

Thermal insulation

Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...

.

Silicones are polymers that include silicon

Silicon

Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 together with carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

, hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, and sometimes other chemical element

Chemical element

A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

s. Some common forms include silicone oil

Silicone oil

A silicone oil is any polymerized siloxanes with organic side chains. They are formed of alternating silicon-oxygen atoms or siloxane, rather than carbon atoms . Other species attach to the tetravalent silicon atoms, not to the divalent oxygen atoms which are fully committed to forming the...

, silicone grease

Silicone grease

Silicone grease is a waterproof grease made by combining a silicone oil with a thickener. Most commonly, the silicone oil is polydimethylsiloxane and the thickener is amorphous fumed silica...

, silicone rubber

Silicone rubber

Silicone rubber is an elastomer composed of silicone—itself a polymer—containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations...

, and silicone resin

Silicone resin

Silicone resins are a type of silicone material which is formed by branched, cage-like oligosiloxanes with the general formula of RnSiXmOy, where R is a non reactive substituent, usually Me or Ph, and X is a functional group H, OH, Cl or OR...

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Some of the most useful properties of silicones include:

• Low thermal conductivity
  Thermal conductivity
  In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
  
  
• Low chemical reactivity.
• Low toxicity
  Toxicity
  Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...
  
  .
• Thermal stability (constancy of properties over a wide temperature range of −100 to 250 °C).
• The ability to repel water and form watertight seals, although silicones are not hydrophobe
  Hydrophobe
  In chemistry, hydrophobicity is the physical property of a molecule that is repelled from a mass of water....
  
  s.
• Excellent resistance to oxygen, ozone, and ultraviolet (UV) light
  Ultraviolet
  Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
  
   such as that in sunlight.