Aramid paper is a high-performance material valued in many industries for its exceptional properties. It is lightweight, heat resistant and offers outstanding electrical insulation capabilities.
Definition of Aramid Paper
Aramid paper is a special insulation material made from aramid fibres. These synthetic fibres belong to the polyamide family and are characterised by their exceptional thermal and mechanical stability.
The structure of aramid paper allows its use in applications where high temperatures, mechanical loads or electrical insulation are required. A well-known example of high-quality aramid paper is Nomex, which is regarded worldwide as the standard in electrical engineering.
Aramid paper from GOBA: supply forms, thicknesses and enquiry
GOBA supplies Aramid paper from a single piece, as material or as a finished part to your drawing.
- Supply forms
- Roll and slit roll, Sheet and board, Cut-to-size, Die-cut part to drawing, Formed part (folded, embossed or bent)
- Thicknesses
- To your specification. GOBA processes materials from 7 µm to 3 mm.
- Versions
- Nomex as standard. Other aramid papers are sourced on customer request.
- Slit rolls
- Widths from 5 to 1,600 mm, tolerance ±0.1 mm, cores of 25, 55, 76 or 152 mm
- Die-cut and formed parts
- Material thickness 0.023 to 3.0 mm, dimensions up to 1,000 × 2,000 mm
- Quantity
- From 1 piece, from sample to series
- Lead time
- Two weeks at most when the material is in stock
What we need for your quotation
- Drawing or dimensions
- Quantity
- Material and thickness
For rolls also width, length, core diameter, core material (for example plastic) and tolerances.
Where is aramid paper used most frequently?
Aramid paper usually sits where a copper winding runs warm and has to be insulated from the lamination stack or from the neighbouring phase. The datasheets of Arclin, which has run DuPont’s Nomex business since 1 April 2026 (Textile World), name motors, generators and transformers as the main applications.
1. Electric Motors and Generators
In the stator the paper lines the slot as slot insulation. In the end winding it separates the phases from each other (phase insulation) and as a slot wedge it closes the slot at the top. Typical slot liners are 0.18 to 0.35 mm thick. Calendered Nomex 410 carries the load when the winding is inserted, uncalendered Nomex 411 with a density of only 0.3 g/cm³ absorbs a lot of impregnating resin and fills voids (Synflex, Nomex 411 datasheet).
2. Transformers
In dry-type transformers aramid paper insulates the layers of the winding from each other and the core from the coil (layer insulation). In liquid-filled transformers aramid appears as Nomex 994 pressboard in spacers and strips. The board absorbs 8 to 10 % of its weight in oil, which is rare for a rigid insulating material (DuPont, Nomex 994 datasheet). Arclin confirms compatibility with mineral and silicone oil and with natural and synthetic esters. Which insulating materials sit in which design is shown in the article on the electrical transformer.
3. Automotive Industry and Electromobility
For traction motors of electric vehicles Arclin now calls Nomex paper the material of choice, mainly because it is compatible with automatic transmission fluid (ATF). In battery packs aramid paper serves as a lightweight flame barrier (CMC Klebetechnik). The insulating parts we make for drives and batteries are described under electromobility and automotive, the particulars of stators with formed wire in the article on hairpin winding.
4. Further Applications
Outside electrical engineering aramid appears mainly as fibre and as honeycomb core. Nomex paper forms the honeycomb cores of sandwich panels in aircraft, fire-resistant protective clothing is made from meta-aramid fibres in fabric, and ballistic vests consist of para-aramid such as Kevlar and Twaron (Wikipedia, Aramide; chemie-schule.de). These products share the chemistry with the insulating paper. Form, density and test values differ, and this article stays with the paper for electrical insulation.
The Main Properties of Aramid Paper
The values below come from the Nomex 410 datasheet (Arclin, issue 04/2026), the most widely used aramid paper. They were measured at 23 °C and 50 % relative humidity. Arclin calls them typical values, not specification limits.
| Property | 0.05 mm | 0.13 mm | 0.25 mm | 0.51 mm | 0.76 mm | Test method |
|---|---|---|---|---|---|---|
| Basis weight | 41 g/m² | 115 g/m² | 249 g/m² | 549 g/m² | 839 g/m² | ASTM D646 |
| Density | 0.72 g/cm³ | 0.88 g/cm³ | 0.96 g/cm³ | 1.06 g/cm³ | 1.08 g/cm³ | calculated |
| Dielectric strength AC, short-term | 18 kV/mm | 28 kV/mm | 33 kV/mm | 32 kV/mm | 27 kV/mm | ASTM D1491 |
| Impulse strength | 39 kV/mm | 55 kV/mm | 63 kV/mm | 55 kV/mm | 49 kV/mm | ASTM D3426 |
| Dielectric constant at 60 Hz | 1.6 | 2.4 | 2.7 | 3.4 | 3.7 | ASTM D150 |
| Tensile strength, machine direction (MD) | 43 N/cm | 141 N/cm | 296 N/cm | 610 N/cm | 816 N/cm | ASTM D828 |
| Tensile strength, cross direction (XD) | 19 N/cm | 71 N/cm | 161 N/cm | 374 N/cm | 592 N/cm | ASTM D828 |
Thermally, Nomex 410 carries the UL rating RTI 220 °C, electrical and mechanical, in all thicknesses from 0.05 to 0.76 mm. The basis is Arrhenius ageing curves that have been confirmed in service for more than 50 years (Arclin). Short-term it can do more: at 400 °C the paper still holds 12 kV/mm for several hours. From 0.13 mm thickness it reaches UL 94 V-0, and its limiting oxygen index drops below the threshold at which it keeps burning in air only between 240 and 350 °C.
Three properties are regularly misjudged in enquiries:
- The table value for dielectric strength is a short-term value. The voltage rises until the paper breaks down after 10 to 20 seconds. For continuous operation in dry-type transformers Arclin recommends no more than 1.6 kV/mm so that no partial discharges start. That is about one twentieth of the table value.
- Thicker does not mean proportionally stronger. Up to 0.18 mm the strength per millimetre rises from 18 to 34 kV/mm, above that it levels off and drops to 27 kV/mm at 0.76 mm. How the property is measured and why it depends on thickness is explained in the article on electrical dielectric strength.
- Moisture costs little voltage but some dimension. At 96 % relative humidity the dielectric strength of 0.25 mm paper only drops from 33.5 to 30.7 kV/mm. Dimensions change more, see the section on processing.
Chemically, aramid paper tolerates the common impregnating varnishes and resins based on polyimide, silicone, epoxy, polyester, acrylic and phenolic, as well as transformer oils and refrigerants. Alcohols, ketones, acetone, toluene and xylene make it swell slightly, similar to water, and this is largely reversed after drying (Arclin). Thermal conductivity at 150 °C lies between 0.10 and 0.18 W/(m·K), on the level of cellulose paper. In the cold the paper gets stronger: at -196 °C tensile strength is 30 to 60 % above the room-temperature value.
Different Types of Aramid Paper
The standard IEC 60819-3-3, in Germany DIN EN 60819-3-3 (VDE 0309-3-3), describes four types of unfilled aramid paper:
- Type 1, calendered, meaning compacted between rolls.
- Type 2, calendered, with improved tear resistance and conformability.
- Type 3, uncalendered.
- Type 4, calendered with lower density, intended for laminating.
In the trade the papers carry brand names. Nomex is the best known, but there are other makers: metastar YT564, for example, is a calendered aramid paper of thermal class H with UL RTI 210 °C in thicknesses of 40 to 130 µm (Synflex, datasheet). The Nomex family at a glance, with the details of each type in the article on Nomex:
| Type | Construction | Thicknesses | Dielectric strength | Use |
|---|---|---|---|---|
| Nomex 410 | calendered, 0.72 to 1.13 g/cm³ | 0.05 to 0.76 mm | 18 to 34 kV/mm | slot, phase and layer insulation, slot wedges (Arclin) |
| Nomex 411 | uncalendered, 0.30 to 0.31 g/cm³ | 0.13 to 0.58 mm | 9 kV/mm | phase insulation, absorbent filler (Synflex, Schweizer) |
| Nomex 414 | calendered, more flexible and conformable than 410 | 0.18 to 0.38 mm | electrically like 410 | phase, slot and layer insulation (Coveme, Schweizer) |
| Nomex 818, formerly 418 | calendered, 50 % mica, 1.13 to 1.18 g/cm³ | 0.08 to 0.25 mm | 28 to 39 kV/mm, continuous up to 3.2 kV/mm | stator coils up to the 13.6 kV class, slot and layer insulation (Arclin) |
| Nomex 356 (E56) | calendered, lighter than 410 | 0.08 to 0.51 mm | below 410 | like 410 at lower stress (Schweizer, CMC) |
| Nomex 992, 993, 994 | pressboard, 994 at 1.15 g/cm³ | 1.0 to 9.6 mm | 994 in oil 27 kV/mm (3.2 mm) | spacers, strips, winding cores (DuPont, Schweizer) |
For insulating parts we usually process Nomex 410. The other types and aramid papers from other makers come in when the insulation system specifies them.
How is aramid paper manufactured?
Aramid paper is made on a paper machine from two forms of the same polymer: short-cut aramid fibres, the floc, and fibrids, fine flat aramid particles (Coveme). The polymer is a meta-aramid, an aromatic polyamide with a density of 1.38 g/cm³, which DuPont has produced industrially since 1966 and named Nomex in 1967 (Wikipedia, Aramide). Without further treatment the result is a loose, absorbent paper of around 0.3 g/cm³, like Nomex 411. Only the calender compacts it into the smooth type 410 paper with 0.72 to 1.13 g/cm³. For Nomex 818, 50 % mica platelets go into the mix.
Because aramid paper is a product of papermaking technology, it has a grain. In machine direction (MD) a 0.25 mm paper carries 296 N/cm, across it (XD) 161 N/cm (Arclin). This direction belongs in the planning of every blank and every punched part.
Advantages of Aramid Paper
For design engineers four points count, each backed by a datasheet value:
- Temperature reserve: 220 °C for the paper, while PET film is rated for class B at 130 °C and electrical pressboard for class A at 105 °C (Synflex, Müller-Ahlhorn).
- Toughness: a 0.25 mm paper stretches 22 % in machine direction before it breaks. It survives winding insertion and folding at the slot edge.
- Resin uptake: the fibre structure absorbs impregnating varnish, so the winding bonds to the slot liner. Synflex names this uptake in laminates with an aramid outer layer as the reason for the good bond between all winding components.
- Fire behaviour: UL 94 V-0 from 0.13 mm and certification to EN 45545-2 for railway vehicles at hazard level HL2 (Arclin).
The usual objection is price. It holds as long as the machine runs in class A or B: there pressboard or PET film do the job, and we recommend them. From class F aramid pays off, mostly as a thin outer layer. In the laminate SynTherm APA/80 only 80 µm of aramid paper sits on each side of a PET film of 50 to 300 µm (Synflex).
Which alternatives to aramid paper exist?
The thermal class decides which alternative fits. The table compares the materials that are available for slot, phase and layer insulation:
| Material | Thermal class | Breakdown | Strength | Source |
|---|---|---|---|---|
| Electrical pressboard (cellulose) | A, 105 °C | at least 9 to 12 kV/mm | low cost, punches well, absorbs oil | Müller-Ahlhorn, IEC 60641 |
| PET film (Mylar A) | B, 130 °C | 19 kV at 0.25 mm, about 76 kV/mm | highest voltage per thickness | Synflex, ASTM D149 |
| NMN laminate (aramid, PET, aramid) | F, 155 °C | at least 10 kV at 0.17 mm, 23 kV at 0.47 mm | film carries the voltage, paper the mechanics | Maier, Trivoltherm N |
| Aramid paper Nomex 410 | RTI 220 °C, in systems mostly H, 180 °C | 33 kV/mm at 0.25 mm, about 8 kV | temperature, toughness, resin uptake | Arclin |
| NKN laminate (aramid, polyimide, aramid) | H, 180 °C | at least 8 kV at 0.20 mm, 11 kV at 0.40 mm | class H with film core | Maier, Trivoltherm NKN |
The table shows the division of labour. Per millimetre, PET film holds more than twice as much as aramid paper. That is why aramid paper is rarely bought for voltage, and why it sits on the outside of laminates: the film in the core holds the voltage, the paper protects it during insertion and takes up the resin. How the paper combines with its neighbours is covered in the articles on pressboard, polyester films, the NMN laminate and Trivoltherm.
The thermal class of a finished insulation system is set by its weakest component. That is why Nomex 410 with RTI 220 °C often appears under class H at 180 °C in distributor lists, and why an NMN with a PET core ends at class F. Above 220 °C polyimide film such as Kapton takes over, from 300 °C only mica in the form of micanite. The whole temperature ladder is set out in the article on high-temperature insulation.
How do you choose the right aramid paper?
We choose in three steps, and the order matters:
- Fix the thermal class of the insulation system. It decides whether aramid is needed at all. Our assignment: class A pressboard 3010 or 3020, class B PET film or DMD, class F NMN or saturated DMD, class H Nomex 410, 411, 414 or NKN, from 220 °C polyimide film. Background in the article on thermal classes.
- Determine voltage and thickness. Calculate with the continuous field strength, not the table value: 1.6 kV/mm for Nomex 410 in dry operation, 1.2 kV/mm for the loose Nomex 411, 3.2 kV/mm for the mica-filled Nomex 818. If that is not enough, a film is added.
- Choose the type by processing. Calendered (410) for parts that are punched, folded and inserted. Uncalendered (411) where resin has to penetrate and fill voids. Mica-filled (818) where partial discharges cannot be ruled out.
On the brand: Nomex has been in use for more than 50 years and is part of many UL-recognised insulation systems (Arclin). Other aramid papers such as metastar have their own UL entries. If your insulation system is listed with a particular paper, check before a switch whether the listing covers the other paper.
Processing aramid paper: slitting, punching, folding
In the tool, aramid paper behaves like a tough technical paper. Two datasheet values decide how we process it. The first is the grain: in machine direction the paper carries almost twice the tensile load it carries across, so we place the machine direction where the tensile force acts on the part. The second is moisture: oven-dry paper grows by up to 1 % in machine direction and up to 2 % across it at 95 % humidity. Under normal room fluctuations the change stays below 1 %, but uneven moisture makes the web cockle. Arclin advises keeping rolls in their PE wrapper until shortly before processing.
- Tapes from the master roll are slit in contract slitting to widths of 5 to 1,600 mm with ±0.1 mm.
- Punched parts are made in material thicknesses of 0.023 to 3.0 mm up to a size of 1,000 x 2,000 mm, with steel rule dies for samples and small series and with solid steel tools on the automatic press for tight tolerances and high volumes.
- The punching tool embosses the fold lines at the same time, so the part can then be bent cleanly into its final shape. Which radii are permissible is shown in the article on the minimum bending radius.
- Water softens aramid paper. Soaked Nomex 818 loses 50 to 70 % of its tensile strength but stretches three times as far and conforms better (Arclin). Complex moulded parts we form under heat.
We fit slot liners to the lamination stack so that they can be inserted at assembly without rework. The processes are described on the pages stamping and forming and insulation and molded parts.
GOBA Takeaway: When aramid paper is the right choice
Aramid paper is the right choice once the winding runs continuously above 130 °C and the part is folded, inserted or mechanically loaded. Below that we recommend pressboard or PET film, because they do the same job at lower cost. Between 155 and 180 °C the laminate is usually more economical, because the film carries the voltage and the aramid is only needed as a thin outer layer. Pure aramid paper pays off where resin has to penetrate, where reserve up to 220 °C is required or where the part has to meet the fire standard for railway vehicles. Our range of aramid papers, laminates and films is listed under insulation materials.
For an enquiry we need three things: the thermal class, the operating voltage and the drawing with thickness and tolerance.
