Electrical Insulation

• A material is known as "electrically conductive" when it allows electrons to propagate through it. Many conductive materials are metals, like copper, although at extremely small scales silicon derivatives may also be used. In contrast, a material is an electrical insulator when it does not allow electricity to flow. Electrical insulators are defined by having a large band gap --- that is, a wide range in which no electrons can exist. This band gap makes electrical transmission difficult, creating an effective insulator.
  
  

Electrical Breakdown

• Despite the existence of band gaps, insulators are generally not perfect. At a certain point, enough electricity is being pushed through the insulated material that the electrical field being generated transforms the insulator into a resistor. At this point, heat buildup begins to take its toll, and eventually the insulator will be completely destroyed. Because of the strength of the currents involved, electrical breakdown is more common in extremely high-voltage applications, where it is also more dangerous.
  
  

Materials

• For situations where extremely high levels of insulation are required, materials like glasses or ceramics may be used. These insulators have a distinctive shape, and some people consider them to be collectors' items. For lower voltage applications, such as are common in hobbyist projects, more flexible materials like rubber or plastic are sufficient. These work by jacketing the wire; alternatively, the wire may be enameled with a thin layer of insulating resin.
  
  

Microelectronic Insulation

• Just like antennas and high-voltage power lines, semiconductor-based microelectronics also require installation --- in this case, to prevent signals from accidentally interfering with one another. For example, printed circuit boards are normally composed of a sheet of resin with a layer of copper on top; circuit designers selectively etch the copper away, leaving behind traces that are insulated from each other by the resin. At the microscopic scale, the same silicon that makes up the computer transistor can act both as a semiconductor and as an insulator: when exposed to oxygen, the silicon forms silicon dioxide, which has natural insulating properties.