A capacitor consists of two conductors separated by an insulator, also known as a dielectric. The properties of the dielectric insulator determine some of the electrical properties of the cable. Tantalum(III) nitride is used as a thin film insulator in some microelectronic fabrication processes. A semiconductor is a material that has a resistivity between a metal and insulator. The material which seals the central electrode to the insulator will boil out. Capacitance occurs between any two conductors separated by an insulator. The inner mitochondrial membrane is both an electrical insulator and chemical barrier. This construct is known as silicon on insulator. A simple barrier can be created by separating two conductors with a very thin insulator. Silicon on insulator (SOI) and silicon on sapphire (SOS) are commonly used. The outer vessel is evacuated with the vacuum acting as a thermal insulator. This is used as a gate insulator and field oxide. Compacted soil is more of a conductor of heat than an insulator. As a durable elastomer, EPDM is conformable, impermeable and a good insulator. Twin-lead consists of a pair of conductors held apart by a continuous insulator.