If you already know NMN and DMD, the next question is almost always NHN. These three flexible composites cover the full thermal ladder for transformer and motor insulation — yet they are easy to confuse on a datasheet because the names differ by a single letter and the structures look alike. This guide completes the picture started in our NMN vs DMD comparison: what NHN actually is, how it sits above NMN and DMD, and how to pick the right grade without over- or under-buying.
What Flexible Composite Insulation Is — in One Line
A flexible composite bonds a thin dielectric film between two outer layers of non-woven or aramid paper. The film carries the dielectric strength; the outer layers add mechanical toughness, absorb impregnating varnish, and survive winding stress. The three-letter code describes the stack — and the stack, especially the core film, decides the temperature class. (For the DMD-vs-NMN basics, see the NMN vs DMD guide.)
DMD: The Class B/F Baseline
DMD = Dacron – Mylar – Dacron — two polyester non-woven layers around a polyester (PET) film core.
- Thermal class: Class B (130°C) up to Class F (155°C) for F-grade versions
- Breakdown voltage: ~8–15 kV/mm
- Cost: lowest of the three
- Best for: general-purpose motors, oil-immersed and dry-type transformer layer/phase insulation, standard industrial equipment below 155°C
DMD is the default when the application sits comfortably below 155°C and budget leads. It handles impregnation well and is widely stocked, which keeps lead times short. See the DMD product page for grades and thicknesses.
NMN: The Class F/H Upgrade
NMN = Nomex – Mylar – Nomex — aramid paper outer layers around the same PET film core.
- Thermal class: Class F (155°C) up to Class H (180°C)
- Breakdown voltage: ~12–20 kV/mm
- Cost: moderate (typically 20–30% above DMD)
- Best for: dry-type (cast-resin) transformers, traction and wind generators, higher-temperature motors, anywhere edge-tear and chemical resistance matter
The aramid outer layers are what you pay for: superior thermal aging, better puncture and tear resistance, and stable performance under thermal cycling. When a design pushes toward or past 155°C, NMN is the natural step up from DMD. Full details on the NMN product page.
NHN: The Class H/C Top Tier
NHN = Nomex – polyimide – Nomex — aramid paper outer layers, but with a polyimide (PI) film core instead of PET.
- Thermal class: Class H (180°C) up to Class C (200–220°C)
- Breakdown voltage: high, with excellent high-temperature retention
- Cost: highest of the three
- Best for: EV traction motors, wind and hydropower generators, aerospace, and any duty that runs hot or cycles hard
The polyimide core is the whole point: it keeps its dielectric and mechanical properties far above where PET film would soften. NHN is the grade you reach for when NMN’s ceiling is not enough. See the NHN product page.
NHN vs NMN vs DMD: Side-by-Side
| Property | DMD | NMN | NHN |
|---|---|---|---|
| Outer layers | Polyester non-woven | Nomex aramid | Nomex aramid |
| Core film | Polyester (PET) | Polyester (PET) | Polyimide (PI) |
| Thermal class | B (130°C) – F (155°C) | F (155°C) – H (180°C) | H (180°C) – C (200–220°C) |
| Breakdown voltage | ~8–15 kV/mm | ~12–20 kV/mm | High, heat-stable |
| Tear / puncture | Good | Superior | Superior |
| Relative cost | Low | Medium | High |
| Typical use | Standard motors, general transformers | Dry-type transformers, traction, high-temp motors | EV traction, wind/hydro, aerospace |
The takeaway: DMD, NMN, and NHN are rungs on one ladder, separated mainly by the core film and therefore by the temperature class.
How to Choose: Three Rules
- Let the hottest spot set the class. Under ~155°C, DMD is usually enough. Cross 155°C and NMN becomes the safe spec. Past 180°C, or under hard thermal cycling, step to NHN.
- Match the duty, not the catalog. A standard LV motor does not need NHN; an EV traction motor does not want to save on a composite that will age early. Specify to the real thermal and mechanical demand.
- Watch thickness separately. All three come in 0.10–0.50 mm ranges. Slot-fill and creepage distance still have to be met — grade and thickness are separate decisions.
Common Specification Mistakes
- Over-specifying: putting NHN in a 120°C appliance motor just because it is “best.” You pay for temperature margin you never use.
- Under-specifying: running DMD where the hotspot reaches 170°C. The composite ages early and you trade a small saving for field failures.
- Confusing NMN and NHN: both are Nomex-faced, but only NHN has the PI core. If the datasheet does not state the core film, ask — the class depends on it.
Conclusion
DMD, NMN, and NHN are not competitors so much as a thermal ladder: DMD for standard Class B/F duty at the best price, NMN for F/H margins, NHN for H/C and the hottest, hardest-cycling duty. Pick by operating temperature and real duty, and you get reliability without paying for unused headroom. Browse the full range in our Flexible Composite Insulation category.
Need help specifying the right composite for your transformer or motor? Contact our team with your temperature class and application — we will match the grade and thickness to your build.
Related reading: NMN vs DMD: How to Choose the Right Flexible Composite Insulation
Browse all flexible composites: Flexible Composite Insulation category