Nomex paper vs Kapton film: which insulation should you use?

In short

Nomex is a calendered aramid paper. Kapton is a polyimide film. Both are high-temperature electrical insulation, but they behave differently: Nomex paper is thicker and more conformable, absorbs impregnating varnish and resin, and is widely used for slot liners and layer insulation in motors, generators and transformers. Kapton film is thin, very high in dielectric strength per thickness, and is often used where space is tight, such as wire wraps, flexible circuits and thin barrier layers.

Typical manufacturer data (examples, not guaranteed limits)

• Nomex 410, 0.25 mm: AC rapid-rise dielectric strength about 33 kV/mm, density about 0.96 g/cm³, UL temperature recognition 220 °C (Arclin Nomex 410 datasheet).
• Kapton 100HN, 25 µm (1 mil): dielectric strength about 303 kV/mm, tensile strength about 231 MPa, electrical relative thermal index 240 °C (Kapton HN product data).
• Dielectric strength figures are short-term test results, not continuous working-voltage ratings.

How to choose

• Need a thicker, tough, resin-impregnable sheet for slot liners, phase or layer insulation: start with Nomex paper.
• Need the thinnest possible high-dielectric barrier, tape wrap or flexible substrate: start with Kapton film or Kapton-based tape.
• Need both: laminates such as Nomex–polyester–Nomex combine properties.
• The final temperature class depends on the complete insulation system, not one material alone.

What to send with your enquiry

• Material and grade if known (for example Nomex 410 or Kapton HN).
• Thickness, width and roll length or cut sheet size.
• Quantity, and whether adhesive is required.
• The application and required temperature class.