Is Rubber a Conductor or Insulator? Understanding the Properties of this Popular Polymer

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Rubber is a very versatile elastomer used in various industries to mold parts and manufacture products such as automotive tires, cables, and surgical gloves. Rubber also serves as a lining material for industrial chutes and storage tanks and a protective coating for various electronics. The question arises: is rubber a conductor or insulator in these applications?

Often, there is confusion on the properties of this polymer and its electrical conductivity. In other words, does it allow or inhibit electricity to flow through it? 

Resolving the question: is rubber a conductor or insulator?

By nature, rubber classifies an insulator because of its molecular structure. As a non-metal, rubber has very few free electrons in its composition. Its atomic structure of tightly bound electrons creates a formidable barrier to the transmission of electrical or thermal energy. This prohibits the polymer from creating an electrical charge or conducting heat.  Therefore, rubber functions effectively as both a thermal and electrical insulator.

In contrast, electrical conductors such as metals and metal alloys, allow electrons or electric charges to flow through. The free movement of electronics allows for an easy charge transfer. For example, aluminum, often used in conjunction with copper, serves as a conductor of electricity in wiring applications. This distinction in properties between rubber and conductive materials like metals helps to address the question “Is rubber a conductor or insulator?”

Importance of Electrical Insulation

Electrical insulators like rubber offer protection from electric shock and electrocution by blocking the flow of energy in unintended directions. For instance, insulated footwear prevents the transfer of electricity from the body to the ground, avoiding an electric shock.

When used as protective sheaths for wires and electronic components, these insulators prevent high voltages from passing into electric circuits, preventing damage, improper performance and safety hazards. Relays and switches also use rubber as an insulator. In addition, electrical insulators reduce the cost of energy while controlling the emissions of pollutants.

Why Rubber is Better

In addition to rubber/elastomers, plastic, wax, glass and Teflon are used as electrical insulators. In many applications, rubber serves as the superior insulator because of its elasticity, ability to withstand deformation under stress, durability, and abrasion resistance.

Often, it is preferred over plastics as it is elastic, resistant to breaking and cracking, and water repellant to provide an excellent grip on wet surfaces. Rubber also offers flexibility in injection molding processes to create different shapes and sizes in parts and is durable against friction, impact, and tearing.

Electrical Insulator Applications

While having different uses, rubber is an ideal electrical insulator for:

  • Wires and cables to prevent shorting or damage.
  • Automotive engines in providing protection from the heat of the exhaust systems.
  • Personal protective equipment to guard against electricity.
  • Footwear soles to reduce the chance of an electrical shock.
  • Electrostatic discharge mats that protect electronic equipment from electrostatic discharges.
  • Mechanical seals and cables used in appliances and vehicles.
  • Electrical components such as wires and circuit boards.
  • Electrical safety mats

Types of Rubber

Rubber is available in both natural and synthetic forms. Both are insulators.

However, each type has different properties that make them better suited for specific applications. For example, natural rubber is strong, flexible, heat-tolerant, and abrasion-resistant. It also resists cutting and adheres to other materials. However, it is vulnerable to fuel, and non-polar solvents such as alkanes, acetic acid and ethyl acetate.

Synthetic rubbers, called elastomers, offer better thermal stability than natural rubber. They also resist high temperatures, chemicals, and oils as well as damage from sunlight, ozone, and weather and maintain strong electrical insulation. In addition, they are often easier to process and function better in a broader range of applications.

While both serve as good insulators, synthetic rubber offers better resistance to heat and the effects of aging. As many types are flame-resistant, they are preferred as insulation for electrical devices.

Synthetic Rubbers Dominate the Market

Statista reports that the global consumption of natural and synthetic rubber in 2022 totaled approximately 29.6 million metric tons. The U.S. is the largest consumer.

Of among the 32 million tons of rubber produced by the U.S. each year, two-thirds are synthetic. The global synthetic rubber market size is estimated to be $23 billion in 2022 and is forecasted to reach $28.9 billion by 2027.

There are many types of synthetic rubber/elastomers. Produced from different formulas of highly versatile materials, each has a distinctive range of properties. A variety of synthetic rubbers exist on the market including:

  • Acrylic
  • Butyl
  • Ethylene
  • Fluoroelastomers
  • Isoprene
  • Nitrile
  • Perfluoroelastomer
  • Silicone

Selecting a synthetic rubber is based on its properties and performance in different applications. Most offer good electrical insulation properties, but have other properties that make them ideal for different applications.

For example, butyl rubber is the only elastomer known to be gas permeable, while silicone rubber is characterized by its resistance to extreme temperatures, fire, ozone and UV radiation.

Synthetic rubbers often are available in different grades.  Silicone rubber also is available in solid and liquid form for greater manufacturing flexibility.  As an example, Wacker Chemical Company provides two distinct grades of silicone rubber:

  • The ELASTOSIL®silicone rubber withstands continuous high temperatures and dynamic stress. Certain grades are suitable for potting or coating applications and manufacturing all types of thermal and electrical insulating devices such as sealants and cables.  Easy to process with good mechanical properties, they are used as sealants in the construction industry and insulators for electronics.
  • The SILPURAN® silicone elastomers are reliable, physiologically safe, incredibly resistant to heat and radiation, and meet high safety standards for the health care industry. The product range includes HTV solid and liquid silicon rubber that ensures the safety and effectiveness of medical devices.

H.M. Royal supplies SILPURAN® and ELASTOSIL® silicone rubber elastomers for a range of applications including those for electrical insulation. To find out more about our silicon rubber products and rubber reinforcement compounds, contact an expert at H.M. Royal today.


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