In modern electric motors, ensuring long-term reliability and electrical safety depends greatly on the insulation system. Among all insulation components, composite insulation papers play a crucial role in slot insulation, phase insulation, liner wrapping, layer insulation, and coil protection. Their combination of electrical strength, thermal stability, and mechanical durability makes them indispensable for both low-voltage and high-performance motors.
This article introduces the six most commonly used composite insulation papers in the motor industry: Fish Paper, DM/DMD, NMN/NM, AHA, NHN, and AMA—explaining their structures, advantages, and typical applications.
Fish paper is a two-layer electrical insulation composite material formed by bonding 100% sulfate wood pulp fiber insulation paper and high temperature resistant electrical insulation polyester film.
Key features include:
• Good mechanical strength
• Stable dielectric properties
• High flexibility and cut-forming capability
It is widely used for slot liners, gasket insulation, and general motor electrical protection. Fish paper remains a popular choice for economical motor designs.
DM/DMD consists of Non-woven cloth bonded with polyester film, forming a three-layer composite.
Advantages:
• Excellent mechanical strength
• Good electrical insulation
• Smooth surface for coil insertion
• Cost-efficient for mass production
DMD is one of the most widely used materials in Class B/F motors, suitable for slot insulation, interturn insulation, and phase insulation.
NMN is a high-performance composite made of Nomex paper + polyester film + Nomex paper, offering significantly improved heat resistance.
Benefits:
• Stable at high temperatures
• High dielectric strength
• Outstanding tear resistance
Ideal for Class F motors, NMN/NM is commonly used in high-speed motors, traction motors, compressors, and industrial pumps where thermal aging resistance is essential.
AHA insulation paper uses double-sided aramid paper with a layer of polyimide film sandwiched in the middle, forming a strong and uniform structure.
Key properties:
• Excellent thermal stability
• Good mechanical endurance
• Reliable bonding strength
AHA is suitable for slot insulation, phase insulation, and layer insulation in motors operating under continuous high temperatures.
5. Class H NHN — Polyimide Film + Nomex® Composite
NHN combines polyimide film (PI) with Nomex® paper, making it one of the premium insulation grades.
Advantages include:
• Exceptional thermal class (up to Class H/200°C)
• High dielectric strength
• Excellent resistance to chemicals and mechanical stress
NHN is the preferred insulation paper for high-end motors, including aerospace motors, servo motors, EV motors, and high-voltage industrial motors.
AMA uses aramid paper + polyester film + aramid paper, creating a balanced structure with enhanced durability.
Features:
• Good heat resistance
• Balanced mechanical and dielectric performance
• Improved structural stability during coil insertion
AMA is widely applied in industrial motors, power tools, pumps, and compressors, providing a strong balance between cost and performance.
Conclusion: Choosing the Right Insulation Paper for Motor Performance
Each composite insulation paper serves different motor designs and performance requirements.
• Fish Paper / DMD → Budget-friendly, suitable for standard motors
• NMN / AHA / AMA → For higher mechanical and thermal demands
• NHN → For premium high-temperature, high-reliability motor applications
At XuJue, we supply all six insulation materials with custom thicknesses, widths, CNC die-cutting, roll-to-sheet processing, and full motor insulation system solutions.
If you need technical support or customized insulation components, feel free to contact us anytime.
