Archive: Mar 2023

Flame Retardant Properties of Polypropylene (Formex, Nomex, Fishpaper)

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Flame retardancy is important in electronic and electrical equipment materials to comply with fire safety standards. Polypropylene is a versatile material with a flame retardant capability, making it popular in various manufacturing applications.

This article will explore the flame retardant properties of polypropylene, specifically Formex, Nomex, and Fishpaper — the three types used by ESPE Manufacturing Co. We will delve into the features behind their flame retardancy and their applications.

What Is Flame Retardancy?

Flame retardant properties are the capacity of a material to hinder the progression of flames or delay the onset of a fire. They are particularly important in industries prioritizing fire safety, such as construction, transportation, and electronics and electrical equipment.

The function of flame-resistant compounds is to inhibit the chemical reactions that occur during combustion. This reduces the material’s combustibility and contribution to the spread of fire.

Numerous techniques exist for applying flame resistance to materials. These include using chemicals, coatings, and flame retardant fibers or fillers within the substance.

Polypropylene Materials

ESPE Manufacturing Co. works with various electrical insulating materials to meet the needs of various applications. Here are some of the materials we employ and provide:


Formex is a type of electrical insulation material made from flame retardant polypropylene. It prevents electrically charged components from arcing and protects the users, equipment, and maintenance personnel. Its properties also ensure that the material will not melt or combust up to 115 °C (239 °F).

This material has received a UL 94V-0 rating, indicating that it meets specific flame resistance criteria and has undergone Underwriters Laboratories (UL) testing. This proves that they do not propagate flames and extinguish them on their own within a few seconds.


Nomex is a meta-aramid material renowned for its ability to resist flames, which can be attributed to its distinctive chemical composition. The material consists of polyamide molecules with long chains, making them highly heat-resistant and difficult to ignite. When exposed to high temperatures, the polymer chains within Nomex link together. This forms a protective layer of char that insulates the material and slows down the combustion process.

This polypropylene type has a wide temperature range from -196 °C (-320 °F) to 250 °C (482 °F) without significant degradation in its mechanical properties. This makes it suitable for high-temperature environments, such as aerospace, marine, electrical, and automotive industries. Furthermore, it has been extensively tested and has received the UL 94V-0 rating.

Fishpaper and Vulcanized Fiber

Fishpaper is an electrical insulation material composed of thin layers of paper that have been treated with a thermosetting resin. The resin acts as a binding agent, holding the layers of paper together and providing the material with its flame retardant properties. Due to this composition, fishpaper has a high flame resistance and is not prone to igniting or supporting combustion.

This material has moderate heat resistance and can withstand up to 120 °C (248 °F). This temperature range is ideal for electrical insulation applications with a moderate heat exposure risk. However, specialized grades can withstand higher temperatures of up to 155 °C (311 °F) or even 180 °C (356 °F). It has also received the UL 94V-0 rating.

Partner With ESPE Manufacturing Co. for Premium Electrical Insulation Materials

ESPE Manufacturing has been a trusted provider of electrical insulators for more than 70 years! We serve a wide range of markets and have a deep understanding of our materials’ unique properties. We also have an expert team that can assist you in selecting the most suitable material for your specific needs.

Contact us today to discover more about our top-quality products and services! You can also request a quote, and we will gladly help you with your needs.

Materials ESPE Works With and Their Dielectric Properties

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Using materials with insulative properties has become crucial due to the increasing need for energy conservation. These materials are often employed in various industrial applications — such as construction, transportation, and packaging — to enhance energy efficiency and reduce overall consumption. They are also crucial in maintaining indoor temperatures, reducing noise pollution, and preventing energy loss.

ESPE Manufacturing Co. is a trusted supplier of electrical insulators, including washers, gaskets, and fabricated plastic parts. We also specialize in the fabrication and conversion of non-metallic materials, allowing us to serve diverse markets and industries.

In this article, we will take a closer look at the materials we at ESPE work with and their respective dielectric properties.

What Are Dielectric Properties?

Dielectric properties are the electrical characteristics of a material that acts as an insulator, impeding the flow of electricity. These properties play a vital role in industries where electrical insulation is critical, such as telecommunications, electronics, and power transmission.

Here are three essential dielectric properties of a material:

  • Dielectric Constant: Also known as relative permittivity, this is the measure of how well a specific material can store electrical energy.
  • Dielectric Strength: This is the maximum electric field strength that a material can withstand before breaking down.
  • Loss Tangent: This is the energy lost as heat when a dielectric material is subjected to an alternating electric field.

Dielectric Materials and Their Properties

ESPE works with several electrical insulating materials to cater to diverse applications. Listed below are some of the materials we use and offer:


Formex is an insulating material recognized for its flame-retardant insulation and adaptability for various applications. It possesses excellent dielectric strength, with 0.010-inch Formex GK having 2200 V/mil strength. This makes it highly resistant to electrical surges. Additionally, it has a UL 94V-0 Flame Class Rating that meets global safety standards.

The exceptional dielectric properties of Formex are further enhanced by its non-hygroscopic quality, which means that it has an extremely low moisture absorption rate of less than 0.06%. This characteristic enables the material to retain its electrical insulation properties for an extended period.


ESPE specializes in the design, production, and distribution of Nomex materials, such as Nomex papers and Nomex pressboards. The formulation of these products involves incorporating meta-aramid polymers into their great, heat-resistant synthetic fibers. As a result, they possess outstanding electrical insulating properties and resistance to chemicals, heat, and radiation.

Nomex Type 410 is an insulation paper providing exceptional dielectric strength, mechanical toughness, flexibility, and resilience. It is available in 12 different thicknesses, ranging from 0.05 to 0.76 mm, for almost any electrical sheet insulation application. Specifically, the 0.010-inch Nomex paper has a dielectric strength of 815 V/mil, making it an excellent choice for high-voltage uses.

Fishpaper and Vulcanized Fiber

At ESPE, we offer a wide variety of vulcanized fiber and fishpaper products. Vulcanized fiber is a chemically pure cellulose material that is environmentally friendly as it contains no adhesives or resins. This low-pressure laminate is produced by reacting cotton or natural wood with various chemicals, including acids, bases, and zinc chloride.

Meanwhile, fishpaper is an insulating board or paper made from vulcanized cotton. It is a flexible material easily cut and shaped to fit around electrical components. As a result, it is commonly used to insulate electric motors, generators, and transformers.

A 0.015-inch vulcanized fiber boasts a moderate dielectric strength of 200 V/mil. It is useful for many electrical insulation applications and can provide adequate protection against electrical surges and breakdowns.

ESPE Manufacturing: Your Trusted Partner for High-Quality Electrical Insulation Materials

At ESPE Manufacturing, we have over 70 years of experience developing and distributing electrical insulators. Our expert team can also help you choose the best material for your requirements, as we cater to multiple markets and understand materials’ distinct properties.

Get in touch with us today to learn more about our products and services or to request a quote. Let ESPE be your trusted partner for all your electrical insulator needs!