Class F vs Class H Composite Insulation Paper: How to Choose

By Chengrui Insulation Material Co.,Ltd
Apr 08 2026

If you are sourcing composite insulation paper for motors, generators or other electrical equipment, one of the most important questions is:

Should you choose Class F or Class H insulation paper?

This is not just a labeling difference. It affects thermal margin, material structure, long-term reliability, and cost.

According to IEC 60085, Class F insulation is rated at 155°C, while Class H insulation is rated at 180°C. That 25°C difference is the core reason these two insulation grades are selected for different applications. In practical terms, Class F composite insulation paper is usually chosen for mainstream industrial motor insulation systems, while Class H composite insulation paper is more suitable for higher-temperature and more demanding operating conditions.

In this guide, we compare Class F vs Class H composite insulation paper from a practical engineering perspective, including temperature class, material structure, common products, applications and selection advice.

1. Quick Answer: Class F vs Class H

If you want the short answer first:

Class F composite insulation paper = 155°C

Class H composite insulation paper = 180°C

Choose Class F when you need a reliable balance of heat resistance, processability and cost.

Choose Class H when the equipment must withstand higher thermal stress, needs more temperature margin, or runs in harsher conditions.

That is the most practical way to understand the difference. IEC 60085 defines those thermal classes, and current industrial guidance consistently positions Class F as the more mainstream 155°C system and Class H as the higher-temperature 180°C system.

2. What Is Composite Insulation Paper?

Composite insulation paper is a flexible laminated insulation material made by combining two or more layers, such as:

polyester film

polyester nonwoven fabric

aramid paper

polyimide film

The purpose of this structure is to combine different performance advantages in one material, including:

electrical insulation performance

mechanical strength

flexibility

thermal endurance

good handling in slot, phase and interlayer insulation

Common examples include:

DMD insulation paper
NMN insulation paper
NHN insulation paper

other polyester- or aramid-based laminated insulation materials

This is why composite insulation paper is widely used in motor winding and generator insulation systems. Your own site already positions DMD, NMN and NHN as key flexible insulation papers under this product family.

3. What Does Class F Mean in Composite Insulation Paper?

In insulation systems, Class F means 155°C.

Class F composite insulation paper is commonly used when the insulation system needs higher thermal resistance than Class B, but does not require the higher cost of Class H materials.

In practical applications, Class F is often associated with:

industrial motors

general generators

winding insulation systems with elevated operating temperature

slot insulation, phase insulation and interlayer insulation

applications where performance and cost must be balanced

On your own site, 6641-F DMD paper is already positioned as a Class F 155°C material, which matches how this product family is commonly sold in the market. Your own recent article also groups 6641-F DMD and some NMN products under Class F materials.

4. What Does Class H Mean in Composite Insulation Paper?

In insulation systems, Class H means 180°C.

Class H composite insulation paper is used where the insulation system must tolerate higher continuous temperature or provide a larger thermal safety margin.

Typical Class H composite insulation papers often involve higher-temperature material systems such as:

aramid paper laminates

Nomex-based laminates

NHN insulation paper

polyimide-based laminates

Your own site’s heat resistance article places 6650 NHN, NMN-H, and AMA-H under Class H 180°C materials, and competitor educational pages currently describe NHN, aramid paper and higher-end laminate systems as the common Class H direction.

5. Typical Material Mapping: Which Papers Are Usually Class F and Which Are Usually Class H?

From a buyer’s perspective, one of the most useful questions is:

Which composite insulation papers are usually Class F, and which are usually Class H?

Common Class F composite insulation paper

DMD insulation paper

some NMN insulation paper

polyester-based laminates designed for 155°C systems

Common Class H composite insulation paper

NHN insulation paper

higher-grade NMN insulation paper

aramid paper laminates

polyimide-based composite papers

Your own site currently shows this pattern clearly: 6641-F DMD under Class F, and 6650 NHN / NMN-H under Class H-related material listings. Recent competitor content also follows the same broad mapping, with DMD and some NMN used in Class F systems, while NHN, aramid paper and polyimide-based materials are used in Class H systems.

That said, buyers should not assume that every product name always equals one thermal class.
The final rating still depends on material construction, adhesive system and insulation system design

6. When Should You Choose Class F Composite Insulation Paper?

Choose Class F composite insulation paper when:

your insulation system is designed for 155°C

the application is standard industrial duty

cost-performance balance matters

you need strong, proven motor insulation without moving into a higher price range

polyester-based laminated insulation is sufficient

Class F is often the practical mainstream choice for many industrial motors and general generators because it provides a good balance of heat resistance and commercial viability. Current educational resources on insulation classes describe Class F this way as well.

7. When Should You Choose Class H Composite Insulation Paper?

Choose Class H composite insulation paper when:

your system is designed for 180°C

the motor or electrical equipment runs hotter

the thermal environment is more severe

you need more thermal safety margin

reliability under heat is more important than lowest material cost

the application is high-load, inverter-related, or otherwise more demanding

Class H materials are commonly recommended for harsher environments and more demanding electrical systems, including heavy-duty motors and high-temperature applications. Current technical guides on thermal classes and motor insulation make the same distinction.

8. Cost vs Performance: Class F or Class H?

In real sourcing, the choice often comes down to cost versus thermal margin.

Class F advantages

lower cost in many cases

widely available

suitable for mainstream motor winding systems

easier to justify in standard applications

Class H advantages

higher thermal capability

larger safety margin

more suitable for harsher environments

stronger fit for premium or high-temperature systems

So if the equipment does not need 180°C capability, Class F may be the smarter buying decision.
But if thermal stress is high, the extra cost of Class H can be justified by better reliability.

9. How to Choose the Right Grade

A practical way to choose is this:

Choose Class F if:

the design target is 155°C
the environment is not extreme
the system is a standard industrial motor or generator
cost control is important

DMD or Class F NMN fits the insulation structure

Choose Class H if:

the design target is 180°C
the equipment runs hotter
extra thermal margin is required
NHN, Nomex-based laminates or other higher-temperature materials are needed
the application is heavy-duty or long-life oriented

In simple words:

Class F is the mainstream performance choice.
Class H is the higher-temperature upgrade.

10.FAQ

Q1:What is the difference between Class F and Class H composite insulation paper?

A: The main difference is thermal class: Class F is 155°C and Class H is 180°C. Class H is used where higher temperature resistance is needed.

Q2: Is DMD insulation paper Class F or Class H?

A: DMD is commonly sold as Class F 155°C in many motor insulation applications, including your own 6641-F DMD product positioning.

Q3: Is NMN insulation paper Class F or Class H?

A: NMN can appear in both Class F and Class H contexts depending on construction and system design, so buyers should always confirm the actual rating on the datasheet.

Looking for reliable composite insulation paper for motors, generators and electrical equipment?

We supply a range of flexible laminated insulation materials, including DMD insulation paper, NMN insulation paper, NHN insulation paper and other custom insulation paper options for industrial applications.