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NOMEX® 410 vs. 411: Choosing Aramid Paper for Motor and Transformer Insulation
Calendered or uncalendered aramid, what DuPont's published numbers say at 10 mil, and how to pick the grade for slot liners, phase insulation and transformer barriers.
For motor slot liners, phase insulation and transformer ground and layer insulation, two aramid papers do most of the work: NOMEX® 410 and NOMEX® 411. They are the same meta-aramid, they carry the same 220 °C thermal recognition, and that is where the resemblance ends. One is calendered into a dense, tough sheet built to hold voltage in the thinnest possible section; the other is left uncalendered so it stays bulky, compressible and absorbent. Specify the wrong one and you either give away slot space you needed for copper, or you put a thin, stiff barrier where the design wanted cushioning and resin pickup.
What aramid paper does inside a motor or transformer
Aramid paper separates conductors from each other and from ground in electrical machines. In a stator it is the slot liner between the copper and the iron, the phase insulation between winding groups, and the wedge or top stick that closes the slot. In a transformer it is the layer insulation between turns, the ground insulation between coil and core, and the spacers and end fillers that hold the coil geometry. The part has to keep its dielectric strength at operating temperature for the life of the machine, survive the mechanical abuse of winding, insertion and varnish cure, and do all of that inside a thickness budget that competes directly with copper for slot fill.
Aramid earns its place because it holds up thermally where cellulose papers and polyester films give out. NOMEX 410 carries a UL 746B relative thermal index of 220 °C for both electrical and mechanical properties, and DuPont reports useful mechanical and dielectric properties from cryogenic temperatures (−196 °C) to about 400 °C. The paper does not melt; it chars at temperatures far above the rating. That is why it is the reference material in so many UL 1446-recognized insulation systems and the default in higher temperature-class designs.
NOMEX 410: calendered, dense, high dielectric per mil
NOMEX® 410 is the original and most widely used grade. After the paper is formed it is calendered, pressed between heated rolls, into a dense, smooth sheet with a density of about 0.96 g/cc at 10 mil and a basis weight of 249 g/m². That density is what buys dielectric strength: 845 V/mil (33 kV/mm) AC rapid rise and 1,600 V/mil (63 kV/mm) full-wave impulse at 10 mil, with a dielectric constant of 2.7 and a dissipation factor of 6 × 10⁻³ at 60 Hz. For a given standoff voltage you can use a thinner liner and give the space back to copper.
It is also the tougher of the two by a wide margin: 296 N/cm tensile in the machine direction and 161 N/cm cross-direction, 22 % and 18 % elongation, 69 N and 42 N initial tear (ASTM D1004) and 5.6 N and 10.6 N Elmendorf tear. That combination is what lets a 410 slot liner take the insertion tooling, the coil pressing and the varnish cure without splitting at a fold. Shrinkage after 300 °C exposure is 0.2 % machine direction and essentially zero cross-direction, so the part stays where it was placed.
410 is produced in ten thicknesses from 2 mil to 30 mil (0.05 to 0.76 mm): 2, 3, 5, 7, 10, 12, 15, 20, 24 and 30 mil. It is UL 94 V-0 at 5 mil and thicker and carries UL 746B RTI 220 °C, electrical and mechanical, in all standard thicknesses. Because it is dense, it is stiffer than 411 at the same thickness; the thin gauges fold cleanly around a scored line, and the thicker gauges are the ones used flat as wedges, barriers and ground insulation. H-O converts 410 into slot liners with scored fold lines, phase insulators, wedges, coil wraps, busbar wraps and layer insulation from sheet and slit rolls.
NOMEX 411: uncalendered, bulky, impregnable
NOMEX® 411 is the uncalendered precursor of 410: the same aramid fibrids and floc, formed into paper and left as it comes off the machine. Without the calendering step the sheet stays open and bulky, with a density of about 0.31 g/cc and a basis weight of 82 g/m² at 10 mil, one third of 410. The electrical and mechanical values fall accordingly: 240 V/mil (9 kV/mm) AC rapid rise, 450 V/mil (18 kV/mm) impulse, 35 N/cm and 20 N/cm tensile, 13 N and 8 N initial tear. Its dielectric constant of 1.2 at 60 Hz tells you how much of the sheet is air.
Those numbers are not a weakness so much as a different job description. The open structure gives 411 high bulk and conformability, so it fills a gap and cushions rather than standing as a thin barrier, and it is far more impregnable and saturable than 410. That is why DuPont positions it for motor phase insulation where the paper has to fill space between winding groups, for transformer coil-end filler and spacers, and for cast-resin turn and layer insulation where the resin is expected to soak through the paper and lock the winding together. It carries the same 220 °C insulating-material recognition as 410, based on DuPont and UL thermal-aging data, and a limiting oxygen index of 28.5 % at room temperature (5 mil), so it will not sustain burning in air.
411 comes in five thicknesses from 5 mil to 23 mil (0.13 to 0.58 mm): 5, 7, 10, 15 and 23 mil. Note the low elongation, 3.4 % machine direction and 5.2 % cross-direction, and the low tear strength: 411 is not the grade for a part that will be pulled through a slot or folded hard on a corner. It works where it is placed, compressed and impregnated.
NOMEX 410 vs 411: the numbers side by side
Published DuPont values for the 10 mil (0.25 mm) grade of each paper, the thickness most often used to compare them. Values at other thicknesses differ; the grade you specify is confirmed against the current DuPont technical data sheet.
| Property (10 mil / 0.25 mm) | NOMEX 410 | NOMEX 411 | Test method |
|---|---|---|---|
| Construction | Calendered | Uncalendered | — |
| Density | 0.96 g/cc | 0.31 g/cc | — |
| Basis weight | 249 g/m² | 82 g/m² | ASTM D646 |
| Dielectric strength, AC rapid rise | 845 V/mil (33 kV/mm) | 240 V/mil (9 kV/mm) | ASTM D1491 / D149 |
| Full-wave impulse strength | 1,600 V/mil (63 kV/mm) | 450 V/mil (18 kV/mm) | ASTM D3426 |
| Dielectric constant, 60 Hz | 2.7 | 1.2 | ASTM D150 |
| Dissipation factor, 60 Hz | 6 × 10⁻³ | 3 × 10⁻³ | ASTM D150 |
| Tensile strength, MD / XD | 296 / 161 N/cm | 35 / 20 N/cm | ASTM D828 |
| Elongation, MD / XD | 22 % / 18 % | 3.4 % / 5.2 % | ASTM D828 |
| Initial tear strength, MD / XD | 69 / 42 N | 13 / 8 N | ASTM D1004 |
| Elmendorf tear, MD / XD | 5.6 / 10.6 N | 1.9 / 2.5 N | TAPPI T414 |
| Shrinkage, MD / XD | 0.2 % / 0.0 % at 300 °C | 0.6 % / 0.9 % at 240 °C | — |
| Standard thicknesses | 2–30 mil (0.05–0.76 mm), ten gauges | 5–23 mil (0.13–0.58 mm), five gauges | — |
| Thermal recognition | UL 746B RTI 220 °C, electrical and mechanical | 220 °C insulating-material recognition | UL 746B |
| Flammability | UL 94 V-0 (5 mil and thicker) | LOI 28.5 % at room temperature (5 mil) | UL 94 / ASTM D2863 |
Read the table as two ratios. Dielectric strength per mil is about 3.5 to 1 in favor of 410; density and bulk are about 3 to 1 in favor of 411. Everything else in the decision follows from those two.
How to choose between 410 and 411
Decide on the binding constraint, not on habit.
- A defined voltage in a tight thickness budget. Slot liners, phase barriers, wedges, ground insulation and transformer layer insulation. Choose 410. Its dielectric density lets the liner go thinner and gives the slot back to copper, and its tensile and tear strength carry it through insertion and pressing.
- Bulk, cushioning or space-filling. Phase insulation that has to fill the gap between winding groups, coil-end fillers, spacers and cushioning layers. Choose 411. It compresses to fit and holds its position without adding a stiff member to the coil.
- Resin or varnish impregnation is part of the design. Cast-resin transformers and vacuum-pressure-impregnated windings where the paper is expected to saturate. Choose 411; its open structure takes resin that calendered 410 largely rejects.
- Handling abuse. A part that is pulled through a slot, folded on a scored line or pressed under tooling wants the 22 % elongation and 69 N tear of 410. The 3.4 % elongation of 411 will not survive that.
- Both jobs in one machine. Use both. A 410 slot liner with 411 coil-end filler, or 410 layer insulation with 411 spacers, is a normal bill of materials, and H-O supplies both from the same order.
The other NOMEX grades: 414, NMN and 818
410 and 411 are the bookends; three other grades H-O converts sit between or beyond them.
| Grade | What it is | Key published values | Where it fits |
|---|---|---|---|
| NOMEX 414 | Calendered under different conditions than 410 for a strong, flexible, conformable sheet; five thicknesses, 3.4–15 mil (0.09–0.38 mm) | 740 V/mil (29 kV/mm) at 10 mil; 229 / 119 N/cm tensile; 7,700-cycle MD fold endurance; density 0.95 g/cc; 220 °C recognition | Slot insulation in hand-wound motors and linear wrapping of wire, where the part is folded and handled more than a machine-inserted liner |
| NOMEX laminate NMN | Triplex of calendered NOMEX bonded to both faces of a polyester film with a high-temperature adhesive; 7–21 mil | NMN 3-5-3 (12 mil): 17,000 V dielectric; 175 / 150 lb/in tensile; 26 / 18 lb tear | UL-recognized insulation systems for Class F and Class H motors and generators, where the film core adds dielectric strength and initial tear and the aramid faces add thermal stability |
| NOMEX 818 | Calendered blend of aramid and mica; five thicknesses, 3–10 mil (0.08–0.25 mm) | 890 V/mil (35 kV/mm) at 5 mil; 700–1,000 V/mil across the range; higher voltage endurance under corona than 410; UL 94 V-0; RTI 220 °C | High-voltage motor conductor and coil wrap, transformer ground and layer insulation where partial discharge, not just breakdown, sets the life |
Where a design has moved past what any aramid paper can do alone, the next steps are the mica barrier sheets and the polyimide films covered in our switchgear busbar and motor insulation guide.
Temperature class, UL recognition and flammability
Three different things get called "the rating," and it pays to keep them apart when a drawing is being written.
- Material thermal index. NOMEX 410 carries UL 746B RTI 220 °C, electrical and mechanical. 411 and 414 carry 220 °C insulating-material recognition based on DuPont and UL thermal-aging data. This is a property of the paper.
- Insulation-system class. A motor or transformer is rated as a system (UL 1446, IEC 60085 thermal classes such as 155 (F), 180 (H) and 220 (R)), and the class belongs to the tested combination of wire enamel, paper, varnish and film, not to any one component. NOMEX 410 appears in systems from Class F upward; NMN laminate is recognized in Class F and Class H systems, the polyester core setting the limit. Substituting a grade inside a recognized system is a system change.
- Flammability and tracking. NOMEX 410 is UL 94 V-0 at 5 mil and above with UL 746A ratings of HWI 0, HAI 0, HVTR 3 and CTI 3; NOMEX 818 is V-0 with HWI 4 and HAI 4. 411 is characterized by limiting oxygen index rather than UL 94 flame class: 28.5 % at room temperature and 21.8 % at 220 °C.
How to spec the die-cut part
H-O does not design insulation systems and does not qualify them; that remains with the machine designer and the system test. What we do is convert the grade you specify, or help you land on one, into the part the winding line needs. The quote goes faster and the part comes out right when the request carries:
- Grade and thickness, or the standoff voltage, test voltage and temperature class if the grade is still open. "NOMEX 410, 10 mil" is a complete material callout; "aramid paper" is not.
- The geometry with fold lines. Slot liners and wraps need the fold locations marked so they can be scored, not just cut. State whether the cuff (the folded-back edge at the slot end) is required and how deep.
- Format. Sheet stock, slit rolls to width for wrapping, precision die-cut components, or kiss-cut parts on a liner for automated insertion. H-O supplies all four in 410, 411, 414, 818 and NMN.
- Laminates and adhesives. If the drawing calls for NMN or another film-cored construction, say so; if a pressure-sensitive adhesive is wanted for placement, name the service temperature so the adhesive does not become the weak point in a 220 °C paper.
- Quantities and traceability. Prototype and production quantities, and whether lot traceability to the DuPont roll certificate is required for the system file.
Aramid paper converts cleanly: 410 die-cuts and scores without fraying, 411 compresses under the tool and is cut with the bulk in mind, and both nest efficiently from sheet when the part outline is known up front. Samples on your geometry typically ship in 3 to 5 business days for common die-cut configurations. For the broader picture of where aramid sits against film, mica and laminate alternatives, see Aramid paper, polyimide film or PEEK for traction motors, Nomex, Kapton, G10 or mica for aerospace machines, and how to spec a custom HV insulation barrier.
Have a slot liner or transformer barrier reviewed
Send the grade and thickness, the standoff voltage and temperature class, and the geometry with fold lines. We will confirm the grade against the current DuPont data sheet, tell you plainly if 411 cannot hold the voltage or if 410 is heavier than the job needs, and convert samples on your geometry.
Samples typically ship in 3 to 5 business days for common die-cut configurations; standard production runs about two weeks; special orders are quoted to the job.
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Frequently asked questions
What is the difference between NOMEX 410 and NOMEX 411?
Both are DuPont meta-aramid papers with the same 220 °C thermal recognition. NOMEX 410 is calendered under heat and pressure into a dense sheet (about 0.96 g/cc at 10 mil), which gives it high dielectric strength and mechanical toughness per unit thickness. NOMEX 411 is the same paper left uncalendered, so it is about one third the density (0.31 g/cc), bulkier, more compressible and more absorbent to varnish and resin, with correspondingly lower electrical and mechanical values.
Which has higher dielectric strength, NOMEX 410 or 411?
NOMEX 410. At 10 mil (0.25 mm) the published AC rapid-rise dielectric strength is 845 V/mil (33 kV/mm) for 410 and 240 V/mil (9 kV/mm) for 411, so 410 holds roughly three and a half times the voltage per mil. Full-wave impulse strength follows the same pattern: 1,600 V/mil for 410 versus 450 V/mil for 411.
Are NOMEX 410 and 411 interchangeable?
No. They share the polymer and the temperature class, but a 411 part specified in place of 410 loses most of the dielectric strength and tensile strength, and a 410 part in place of 411 loses the bulk, cushioning and resin absorption that 411 was chosen for. Treat them as two materials that happen to share a name, and change grade only with the insulation-system engineer's sign-off.
When should I use NOMEX 411 instead of 410?
Use 411 where bulk and conformability matter more than dielectric strength per mil: motor phase insulation that has to fill a gap, transformer coil-end filler and spacers, cushioning between layers, and cast-resin turn and layer insulation where the paper is expected to saturate with resin. Where the part is a thin barrier holding off a defined voltage, such as a slot liner or ground insulation, 410 is the default.
What temperature is NOMEX paper rated for?
NOMEX 410 carries a UL 746B relative thermal index of 220 °C for both electrical and mechanical properties, and DuPont reports useful mechanical and dielectric properties from cryogenic temperatures (−196 °C) up to about 400 °C. NOMEX 411 and 414 carry 220 °C insulating-material recognition based on DuPont and UL thermal-aging data. Aramid does not melt; it chars at temperatures well above the rating.
What thicknesses do NOMEX 410 and 411 come in?
NOMEX 410 is produced in ten thicknesses from 2 mil to 30 mil (0.05 to 0.76 mm): 2, 3, 5, 7, 10, 12, 15, 20, 24 and 30 mil. NOMEX 411 is produced in five thicknesses from 5 mil to 23 mil (0.13 to 0.58 mm): 5, 7, 10, 15 and 23 mil. H-O supplies both as sheet stock, slit rolls, precision die-cut components and kiss-cut parts on a liner.
Is NOMEX paper flame resistant?
Yes. NOMEX 410 is UL 94 V-0 at 5 mil and thicker, and the aramid-mica grade NOMEX 818 is also V-0. NOMEX 411 has a limiting oxygen index of 28.5 % at room temperature (5 mil), which means it will not sustain burning in normal air. None of the grades melt or drip.
Can H-O die-cut NOMEX slot liners and phase insulation to my drawing?
Yes. H-O die-cuts, kiss-cuts and slits NOMEX 410, 411, 414, 818 and NMN laminate in Winsted, Connecticut, including slot liners with scored fold lines, phase insulators, wedges, coil wraps and layer insulation. Send the grade and thickness, the standoff voltage and temperature class, the geometry with fold lines and the quantities; engineering confirms the grade against the current DuPont data sheet and quotes samples through production.
Request a quote for your NOMEX® slot liners, phase insulation or barriers
Send H-O the grade and thickness (or the standoff voltage and temperature class if the grade is still open), the slot or coil geometry with fold lines, and quantities. Engineering reviews every RFQ, confirms the grade against the current DuPont data sheet, and converts samples on your geometry.
Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
References
- DuPont. NOMEX® Paper Type 410 Technical Data Sheet. Typical properties by thickness, UL recognitions. The current sheet is linked from the NOMEX 410 product page.
- DuPont. NOMEX® Paper Type 411 Technical Data Sheet. Linked from the NOMEX 411 product page.
- DuPont. NOMEX® Paper Type 414, NOMEX® Laminate Type NMN and NOMEX® 818 technical data sheets. Linked from the 414, NMN and 818 product pages.
- UL 746B, Polymeric Materials – Long Term Property Evaluations (relative thermal index). UL 746A, Polymeric Materials – Short Term Property Evaluations (HWI, HAI, HVTR, CTI). UL 94, Tests for Flammability of Plastic Materials. UL 1446, Systems of Insulating Materials – General.
- IEC 60085, Electrical insulation – Thermal evaluation and designation (thermal classes 155, 180, 220).
- ASTM D149 and D1491 (dielectric strength), ASTM D3426 (impulse), ASTM D150 (dielectric constant and dissipation factor), ASTM D828 (tensile and elongation), ASTM D1004 (initial tear), TAPPI T414 (Elmendorf tear), ASTM D2863 (limiting oxygen index).
NOMEX® is a registered trademark of DuPont de Nemours, Inc. or its affiliates. Property values quoted in this article are typical published values from the manufacturer's technical data sheets at the stated thickness, are not specifications, and are confirmed against the manufacturer's current data sheet at the time of order.
H-O Products is a precision die-cut converter of electrical insulation materials, not a raw-material producer; we do not design, test or certify insulation systems. Insulation-system class, dielectric test levels and qualification remain the responsibility of the machine designer and the applicable UL or IEC system evaluation.
H-O Products is an ISO 9001:2015 certified organization; that certification covers our quality management system, not individual materials or parts. Grade-specific values are confirmed against the manufacturer's current technical data sheet and an engineering drawing review. All parts are custom manufactured to order and minimum production run quantities apply.