What is the Best Insulator?

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An insulator, also called a dielectric, is a substance that resists the flow of electric current. The atoms of an insulating material have atoms with tightly bonded valence electrons which cannot readily move. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate electrical conductors without passing current through themselves.

You must have seen those brown shiny devices around you on an electric pole, on transformers and even in electric trains. They are called insulators. Ever wonder why they come in such peculiar shapes and why they are used. The insulators provide necessary insulation between line conductors and supports, preventing any leakage current from conductors to earth.

The main function of an insulator is to resist any leakage current. Thus it must have very high insulation resistance. Also, the dielectric strength of the insulators must be very high.


Like most technological advances, it happened by accident in the early 30s. In 1932, a researcher named Dale Kleist attempted to create a vacuum seal between two glass blocks while using a jet of high-pressure air. Surprisingly, the high-pressure air turned a stream of molten glass into fine fibers. These fibers eventually became the base of fiberglass insulation. Fiberglass was trademarked in 1938 and was subsequently used in clothing, fishing rods, boat hulls, and automobile bodies.

How insulators work?

Thermal insulation resists and restricts heat transfer via three mechanisms: conduction, convection and radiation. Conduction is how heat is transmitted between neighboring atoms or molecules through collisions; convection is heat transfer by the bulk movement of molecules within fluids such as air or water; radiation is heat transfer across space from one body to another as energy. Insulators have strong bonds that hold their particles tightly in place. 

Are insulators good conductors of heat?

Conductors are materials that allow thermal energy to flow easily through it whereas insulators are substances that restrict the flow of thermal energy transfer through it. Metals, for example, are great conductors and are commonly used materials for cooking dishes. Paper, wood and Styrofoam are good insulators and are commonly used to keep the food hot or cold and are commonly used as cooking utensils. Insulators oppose electrical current, hence make poor conductors.

Can insulators be polarized?

Electrons are not allowed to jump from atom to atom. They have to stick to the atom they are on unless in extreme circumstances when you’re lighting the insulator on fire or trying to pass current through it. Conductors can be polarized because charges are free to roam where insulators are not able to bring charge from one end to the other easily. Insulators cannot be polarized like the dielectrics in the presence of electric field.

Can insulators be charged?

Insulators can be charged only by friction i.e. by rubbing together. The material that gives electrons gets positively charged whereas the material that takes electrons gets negatively charged. They serve a critical role in electrostatic experiments and demonstrations. However, insulators cannot be charged by induction because they have less negatively charged electrons than positively charged protons.

The most effective and common electrical insulators are rubber, glass, oil, air, diamond, and so on.

Ceramic – For example, ceramic is a good thermal insulator and does not expand greatly when heated. Well, most people do not associate ceramics with electrical applications, but a large number and variety of ceramic compounds are electrical insulators. Thanks to its long life and its ability to hold shape and size under pressure, it is a great insulating material for heated applications.

Wood – Wood is also a good insulator, even better than glass because it has several pores in it which act as tiny air traps that resist the transfer of heat. So, wood and wood base materials are naturally good insulators of heat compared to other materials like marble, metals and concrete. 

Water – Water is a poor conductor of heat but a good conductor of electricity, until or unless it’s 100% pure water. Pure water does not contain any impurities such as sodium, calcium, magnesium and other salts which behave as charge carriers. So, it does not conduct electricity. In other words, if electrolytes are present in water, it acts as a conductor.

Copper – Copper is a conductor, not an insulator. It is predominantly used as a material for wires because it is a very good conductor of electric current. Copper is probably the most common and cheaper conductor that works best in electrical equipment such as wires and motors. It is a major industrial metal because of its high thermal and electrical conductivity.

Which insulator is used in overhead lines?

The most commonly used insulating material for overhead line is porcelain, but glass, steatite and special composite materials are also used to a limited extent. Insulators made from porcelain exhibit excellent properties such as high electrical stability, high mechanical strength and corrosion resistance.

What is Wall Insulation?

Do you know about one third of heat lost from an uninsulated home escapes through the walls. External wall insulation is a thermally insulated, protective barrier that keeps the heat in and the cold out. Depending on the type of wall you can add insulation to the inside or outside or even in between. It puts a cladding between your living area and the extreme outdoor temperatures. By properly insulating walls, you can save energy and cut costs off your electricity bill.

Why insulators cannot conduct electricity?

The atoms of an insulating material have atoms with tightly bonded valence electrons which cannot readily move because molecules are far from each other compared to conductors. Hence, electric charge cannot move freely through the material. So, insulators do not allow electricity to pass through.

Which material is used as electrical insulator?

Some of the common examples of electrical insulators are porcelain, mica, Teflon, plastic, paper, rubber, ceramic, glass, etc.

Difference between insulator and conductor

Conductors are materials that allow the electric current or heat to pass through them whereas insulators do not allow electric current or heat to pass through them. Conductors allow free flow of electrons from one atom to another, while insulators are materials that impede the free flow of electrons from atom to atom and molecule to molecule.

What is strain insulator?

Strain insulator is a type of insulator used for handling the mechanical stresses at angle positions of the line i.e. corner or sharp curve, end of lines, intermediate anchor towers, and long river crossings. The discs of a strain insulator are same as that of a suspension type insulator but are arranged on a horizontal plane.


The main function of the insulator is to provide perfect insulation between the live conductors and the supports and to prevent any leakage current from the live conductors to earth through the supports. Insulators are substances that keep electricity or heat from easily transferring through. Plastic, wood, rubber and glass are good insulating materials. You can found insulators mostly on household items and electrical circuits as protection. Thermal insulation is a related concept, but restricts the flow of heat instead of electricity.


Arora, Ravindra and Wolfgang Mosch. High Voltage and Electrical Insulation Engineering. New Jersey, United States: John Wiley & Sons, 2011. Print

Dunlop, Carson. Principles of Home Inspection: Systems & standards. Illinois, United States: Dearborn Real Estate Education, 2003. Print

Kośny, Jan and David W. Yarbrough. Thermal Insulation and Radiation Control Technologies for Buildings. Berlin, Germany: Springer, 2022. Print

Author: Sagar Khillar

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