Nomex® 818 Calendered Aramid-Mica Insulation Paper
Nomex® 818 is a calendered blend of aramid and mica paper designed for high-voltage applications, including motor conductor and coil wrap, transformer ground and layer insulation. It offers high inherent dielectric strength (700–1,000 V/mil) and increased voltage endurance compared to Nomex® 410 when subjected to corona attack. Nomex® 818 is available in five thicknesses ranging from 0.08 mm to 0.25 mm (3 mil to 10 mil).
Key Properties
- Tensile Strength (0.13 mm/5 mil): MD 52 N/cm, XD 38 N/cm — ASTM D828
- Elongation (0.13 mm/5 mil): MD 3.0%, XD 3.4% — ASTM D828
- Dielectric Strength, AC Rapid Rise (0.13 mm/5 mil): 890 V/mil (35.0 kV/mm) — ASTM D149
- Temperature Resistance: Recognized 220°C insulating material; retains ≥50% tensile strength and elongation up to 250°C
- Thickness Range: 0.08–0.25 mm (3–10 mil), 5 standard grades — ASTM D374
- Density (0.13 mm/5 mil): 1.13 g/cc
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- Specifications
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Electrical Properties (0.13 mm/5 mil)
| Property | Value | Test Method |
| Dielectric Strength, AC Rapid Rise | 890 V/mil (35.0 kV/mm) | ASTM D149 |
| Full Wave Impulse | 1,600 V/mil (63 kV/mm) | ASTM D3426 |
| Dielectric Constant at 60 Hz, 50% RH | 3.6 | ASTM D150 |
| Dielectric Constant at 60 Hz, Dry | 2.5 | ASTM D150 |
| Dissipation Factor at 60 Hz, 50% RH | 120 x10⁻³ | ASTM D150 |
| Dissipation Factor at 60 Hz, Dry | 6 x10⁻³ | ASTM D150 |
| Volume Resistivity, 50% RH | 10¹³ ohm·cm | ASTM D257 |
| Volume Resistivity, Dry | 10¹⁶ ohm·cm | ASTM D257 |
| Surface Resistivity, 50% RH | 10¹² ohm/square | ASTM D257 |
| Surface Resistivity, Dry | 10¹⁵ ohm/square | ASTM D257 |
Mechanical Properties (0.13 mm/5 mil)
| Property | Value | Test Method |
| Typical Thickness | 0.13 mm (5.2 mil) | ASTM D374 |
| Basis Weight | 148.4 g/m² | ASTM D646 |
| Density | 1.13 g/cc | — |
| Tensile Strength, MD | 52 N/cm | ASTM D828 |
| Tensile Strength, XD | 38 N/cm | ASTM D828 |
| Elongation, MD | 3.0% | ASTM D828 |
| Elongation, XD | 3.4% | ASTM D828 |
| Elmendorf Tear, MD | 2.0 N | TAPPI 414 |
| Elmendorf Tear, XD | 2.9 N | TAPPI 414 |
| Initial Tear Strength, MD | 16 N | ASTM D1004 |
| Initial Tear Strength, XD | 10 N | ASTM D1004 |
| Shrinkage at 300°C, MD | 0.1% | — |
| Shrinkage at 300°C, XD | 0.0% | — |
Environmental Performance (0.25 mm/10 mil, 2 MeV Beta Radiation)
| Property | Value | Test Method |
| Tensile Strength Retention after 64 Mgy, MD | 88% of original | ASTM D828 |
| Tensile Strength Retention after 64 Mgy, XD | 78% of original | ASTM D828 |
| Dielectric Strength after 64 Mgy | 1,320 V/mil | ASTM D149 |
Regulatory / Compliance Data (0.13 mm/5 mil)
| Property | Value | Test Method |
| UL 94 Flame Class | V-0 | — |
| UL 746A HWI Rating | 4 | — |
| UL 746A HAI Rating | 4 | — |
| UL 746B RTI, Electrical | 220°C | — |
| UL 746B RTI, Mechanical | 220°C | — |
| UL 746A HVTR Rating | 3 | — |
| UL 746A CTI Rating | 3 | — |
Compliance
- UL 94 V-0 — Compliant (0.08–0.25 mm / 3–10 mil)
- UL 746B RTI 220°C, Electrical and Mechanical — Compliant (0.08–0.25 mm / 3–10 mil)
- High-voltage motor conductor and coil wrap
- Transformer ground insulation
- Transformer layer insulation
- Stator coil insulation in AC motors up to 13.6 kV class
- High-voltage equipment requiring corona and voltage-endurance resistance
Common industries: high-voltage motor manufacturing, transformer manufacturing, industrial electrical equipment.
Nomex® 818 is a calendered blend of aramid and mica engineered specifically for high-voltage applications such as motor conductor and coil wrap, and transformer ground and layer insulation. Because it is composed of 50% inorganic mica, its dielectric properties are markedly more stable with temperature than standard aramid paper, and its dielectric constant remains essentially unchanged from 23°C to 250°C.
Nomex® 818 is designed to provide voltage endurance under sustained corona attack at least equivalent to the best inorganic insulations, and greatly superior to other organic materials, which has led to its long-standing commercial use insulating stator coils in AC motors up to 13.6 kV class. Its Limiting Oxygen Index is 63% at room temperature, declining to 52% at 220°C, and it must be heated above 700°C before its LOI falls below the flammability threshold.
Compliant with UL 94 V-0 and UL 746B RTI ratings of 220°C (Electrical and Mechanical).
What differentiates Nomex® 818 from Nomex® 410?
Nomex® 818 is a calendered blend of aramid and mica offering higher inherent dielectric strength (700–1,000 V/mil) and significantly increased voltage endurance under corona attack compared to Nomex® 410, making it the preferred choice for high-voltage motor and transformer insulation.
Why does tensile strength matter for film selection?
Nomex® 818's tensile strength (up to 111 N/cm MD at 10 mil) ensures the material withstands the mechanical stresses of coil winding and wrapping during high-voltage motor and transformer manufacturing without tearing.
What is the operating temperature range for Nomex® 818?
Nomex® 818 is recognized as a 220°C insulating material and retains at least 50% of its room-temperature tensile strength and elongation at temperatures up to 250°C.
Is Nomex® 818 suitable for high-voltage regulated electrical environments?
Yes. Nomex® 818 carries a UL 94 V-0 flame class and UL 746B RTI ratings of 220°C (Electrical and Mechanical), and has been used commercially to insulate stator coils in AC motors up to 13.6 kV class.
How should Nomex® 818 be specified?
Specify grade (Nomex® 818), thickness, compliance requirements, dimensional tolerances, and finished format.
