An insulator is a material or method that restricts the transfer of either heat or electricity. In the case of heat, thermal insulators work by reducing the rate heat can travel through a space. Generally, they use specific materials and will keep heat-carrying matter from moving. In the case of electricity, electrical insulators confine an electric current to a designated path. They typically work by using a material with many outer elections, a condition that will cause low electrical conductivity.
The first sense of an insulator is the thermal sense. A thermal insulator helps keep an object at the same temperature, whether hot or cold. It typically works by addressing either conduction or convection, which are two modes of heat transfer. Conduction is heat that moves through a material whose atoms are stationary; this type refers to the heat that can travel through a piece of solid metal. Convection, on the other hand, is internal heat carried with moving matter; this occurs when wind carries heat away from one’s body.
A thermal insulator functions by slowing the rate heat can move through a region. The rate of conductive heat transfer is proportional to a material property called thermal conductivity—copper, for example, transfers heat quickly because of its high-thermal conductivity. A good insulator, therefore, has a low-thermal conductivity. In fact, air has a low conductivity, but it tends to move around a lot. Using a blanket works as a thermal insulator because it forces air to transfer heat through conduction instead of convection.
The second sense of an insulator is electrical. An electrical insulator does not permit an electric current to flow through it because it has a low electrical conductivity. Many factors affect electrical conductivity, including temperature, but elements tend to have either high or low conductivity. This results because different elements have a different number of outer electrons, which changes how easy it is to free those electrons. Metals, for example, tend to have high conductivity because their outer electrons are easy to free.
Many other elements and compounds have a high number of outer electrons, making them difficult to free. This is generally the case for glass, plastic, porcelain and rubber. Therefore, these materials are used in electrical appliances to keep electrical currents on a restricted path. Low electrical conductivity is also a property of air and many other gases. Air is the only insulator used on raised power lines.