Nomex paper shows up in almost every high-temperature motor, generator and dry-type transformer. But ask a supplier for Nomex and the first question back is usually which grade: 410 or 411. The two look alike on the roll, yet they behave quite differently in a winding.
This guide explains how the two most common DuPont Nomex paper grades differ, where each one fits, and how to choose between them.
What Is Nomex Paper?
Nomex is a meta-aramid paper originally developed by DuPont. It is made from short aramid fibres and binders formed into a sheet. Aramid does not melt, resists flame, and keeps its electrical and mechanical properties at temperatures that would char ordinary cellulose paper. Nomex papers are commonly rated for continuous use up to around 220°C, which puts them comfortably in Class H insulation systems.
The grade number tells you how the sheet was finished after forming, and that finishing changes almost everything about how it behaves. For a wider introduction, see our page on Nomex paper and our full range of aramid papers.
Nomex 410: The Calendered Grade
Nomex 410 is pressed between heated rollers after forming, a process called calendering. That densifies the sheet and gives it a smooth, hard surface.
The result is a strong, dense paper with:
- high dielectric strength for its thickness
- high tensile and tear strength, so it survives slot insertion and tight bends
- a smooth surface that slides easily into motor slots
- low absorption of resin and varnish
410 is the most widely used Nomex grade. Typical jobs include slot liners, slot closures and wedges, phase separators, end-turn insulation in motors and generators, and layer insulation in dry-type transformers. It is also the paper layer in many laminates. See our pure Nomex aramid paper 410 and Nomex 410 insulation paper for motor winding.
Nomex 411: The Uncalendered Grade
Nomex 411 skips the calendering step. The sheet stays lower in density, softer and more open.
That changes its character:
- it soaks up varnish and resin readily, so impregnation reaches right through it
- it conforms to irregular shapes and acts as a cushion
- its dielectric strength is lower than 410 of the same thickness
- it is less stiff and less strong in tension
Those traits make 411 the choice where full resin saturation matters, such as coil wraps and layer insulation that will be vacuum pressure impregnated or cast. It is also used as padding and as a soft layer in some laminates. See our uncalendered Nomex aramid paper 411.
Nomex 410 vs 411 at a Glance
| Feature | Nomex 410 | Nomex 411 |
| Finishing | Calendered (hot-pressed) | Uncalendered |
| Density | Higher | Lower |
| Surface and feel | Smooth, firm | Soft, fibrous |
| Dielectric strength for the same thickness | Higher | Lower |
| Resin and varnish absorption | Low | High |
| Conformability | Moderate | High |
| Typical uses | Slot liners, wedges, phase and layer insulation, laminates | Coil wraps, impregnated layer insulation, padding |
Both grades share the same aramid base, so they offer the same high-temperature capability. The difference is in density and finish, not heat resistance.
Which Grade Should You Use?
- The paper must carry voltage in a tight space. Choose 410. It gives more dielectric strength per millimetre.
- The paper will be pushed into slots or bent sharply. Choose 410 for its strength and smooth surface.
- The winding will be varnished or VPI and needs full resin penetration. Choose 411, or combine it with 410 so the resin can bond the layers.
- The surface is irregular or needs cushioning. Choose 411.
- You are unsure. In most motor and generator work, 410 is the default. 411 is a specialist grade picked for impregnation and conformability.
For a broader look at winding papers, read our guides on types of insulation paper for motor winding and transformer insulation materials.
Alternatives and Laminates
Nomex is not the only aramid paper. Other manufacturers make calendered and uncalendered grades that play the same roles. We supply Metastar YT 510 (calendered) and YT 511 (uncalendered), as well as pure aramid paper X630 and uncalendered aramid paper X611. Compare datasheets for dielectric strength, density and thickness when you switch.
Where you need more dielectric strength than paper alone, aramid paper is laminated with film. NMN insulation paper sandwiches polyester film between two aramid layers, and AMA insulation paper is another common build. See our full range of laminated insulation paper composites. For taping jobs, our Class H aramid paper adhesive tapes use the same base material.
The Short Answer
Nomex 410 is the dense, calendered workhorse for slot liners, phase separators and layer insulation where strength and dielectric performance matter. Nomex 411 is the soft, uncalendered grade for windings that must absorb resin or fit around irregular shapes. Many Class H designs use both.
Harnawa supplies both grades along with equivalent aramid papers and laminates. Contact us with your application, thickness and insulation class, and we will help you pick the right paper.
Frequently Asked Questions
What is the difference between Nomex 410 and Nomex 411?
Nomex 410 is calendered, so it is dense, smooth and strong, with higher dielectric strength. Nomex 411 is uncalendered, so it is softer, more conformable and absorbs resin and varnish much more readily.
Which Nomex paper is used for motor slot liners?
Nomex 410 is the usual choice for slot liners, slot closures and phase separators because of its strength, smooth surface and high dielectric strength.
What is the temperature rating of Nomex paper?
Nomex papers are commonly rated for continuous use up to around 220°C, which makes them suitable for Class H insulation systems and above.
When should I use Nomex 411?
Use Nomex 411 where resin or varnish must soak right through the insulation, such as VPI or cast windings, or where the paper must conform to irregular shapes.
Is Nomex the same as aramid paper?
Nomex is a brand of meta-aramid paper. Other manufacturers make aramid papers that serve the same purpose, such as Metastar YT 510 and YT 511.
Is Nomex 410 calendered?
Yes. Nomex 410 is calendered, which gives it its high density and smooth surface. Nomex 411 is the uncalendered grade.
