Silicone is an inert synthetic compound typically heat-resistant and rubber-like polymers that include silicone together with carbon, hydrogen, oxygen, and sometimes other elements. Some common forms include silicone oil, silicone grease, silicone rubber, silicone resin, and silicone caulk. Silicones exhibit many useful properties, including: Low thermal conductivity, Low chemical reactivity, Low toxicity, Thermal stability, Does not support microbiological growth, Resistance to oxygen, ozone, and ultraviolet (UV) light. Silcone has a high gas permeability at room temperature (25 °C), the permeability of silicone rubber for such gases as oxygen is approximately 400 times that of butyl rubber, making silicone useful for medical applications in which increased aeration is desired. Consequently, silicone rubbers cannot be used where gas-tight seals are necessary.