Nomex® Paper Properties

Article | August 13, 2014
Nomex® Paper Properties

DuPont™ Nomex® brand products provide high levels of electrical, chemical and mechanical integrity, making them ideally suited for a broad range of electrical insulation applications. 

In fact, for more than 50 years, manufacturers of transformers, generators, motors and other electrical equipment have relied on the unique combination of Nomex® paper properties to help optimize performance, increase reliability and extend the service life of their own products. 

The unique combination of Nomex® paper properties—which is unmatched by competitive products—includes:

• Inherent dielectric strength
• Mechanical toughness
• Thermal stability
• Chemical compatibility
• Radiation resistance
• Flame resistance
• Moisture insensitivity
• Cryogenic capabilities

Inherent Dielectric Strength

In densified form, Nomex® products withstand short-term electrical stresses of 18 kV/mm to 34 kV/mm (460 V/mil to 870 V/mil), depending on product type and thickness.

Mechanical Toughness

Densified Nomex® products are strong, resilient and (in the thinner grades) flexible, with good resistance to tearing and abrasion.

Thermal Stability

Temperatures up to 200°C have little or no effect on the electrical and mechanical properties of Nomex® products.  Useful Nomex® paper properties are retained at considerably higher temperatures.  These useful Nomex® paper properties are maintained for at least 10 years of continuous exposure at temperatures up to 220°C.

Chemical Compatibility

Nomex® products are essentially unaffected by most solvents and are unusually resistant to attacks by acids and alkalis.  They are compatible with all classes of varnishes and adhesives, transformer fluids, lubricating oils and refrigerants.  Because Nomex® products are not digestible, they are not attacked by insects, fungi or mold.

Radiation Resistance

Nomex® paper is essentially unaffected by 800 megarads (8 Mgy) of ionizing radiation and still retains useful mechanical and electrical properties after eight times this exposure.

Flame Resistance

Nomex® products do not produce known toxic reactions in humans or animals.  Nomex® products do not melt and, with a limiting oxygen index (LOI) at 220°C above 20.8—the critical value for combustion in air—they do not support combustion.  Nomex® products fulfilling UL 94V-O requirements are available.

Moisture Insensitivity

In equilibrium at 95% relative humidity, densified Nomex® papers and pressboards maintain 90% of their bone-dry dielectric strength, while many of their mechanical properties are actually improved.

Cryogenic Capabilities

Nomex® products have found acceptance in a variety of cryogenic applications due to their unique polymer structure.  At the boiling point of nitrogen (77 K), Nomex® 410, Nomex® 993 PSB and Nomex® 994 PSB have tensile strengths in excess of room temperature values.

Not all styles of Nomex® paper have the same characteristics across these performance categories.  These characteristics typically apply to the products in the Nomex® 400 Series.  For other Nomex® papers and pressboards, please refer to the specific product specifications.