Diamond Dotted Paper vs Crepe Paper for Transformers: Key Differences

When selecting insulation materials for transformer manufacturing, two commonly discussed  transformer insulation papers are diamond dotted paper and crepe paper. Both are used in transformers, but they are designed for different jobs and should not be treated as interchangeable.

If you only want the short answer:

• Diamond dotted paper is mainly used for interlayer insulation with bonding and winding stability

• Crepe paper is mainly used for flexible insulation on curved, uneven or irregular transformer parts

That is the main difference. If the job is to hold winding layers together, diamond dotted paper is usually the better choice. If the job is to wrap leads, corners or irregular surfaces, crepe paper is usually the better choice.

For transformer manufacturers and insulation buyers, the real question is not which paper is “better” in general. The real question is:

Which paper is better for the specific transformer part and production process?

1. What Is Diamond Dotted Paper?

Diamond dotted paper, often called DDP, is made from insulation press paper that is partially coated with epoxy resin in a dotted pattern on one or both sides. The resin is dry and non-tacky during storage and handling, but during winding drying and curing it softens and bonds adjacent layers together.

That structure gives DDP several practical functions inside a transformer winding:

interlayer electrical insulation

bonding between winding layers

better winding integrity

reduced layer movement under stress

support for evacuation of air and moisture during drying

support for oil impregnation through the open channels between resin dots

In other words, diamond dotted paper is not just an insulation paper. It is an insulation and bonding paper.

2. What Is Crepe Paper?

Crepe paper is a cellulose-based transformer insulation paper with a crinkled structure that gives it flexibility and stretch. Its main purpose is not bonding. Its main value is that it can conform to shapes that flat papers cannot wrap well.

Crepe paper is commonly used for:

lead insulation

wrapping conductors and local parts

covering corners and edges

insulating curved or uneven surfaces

applications where flat paper cannot fit properly

Public transformer insulation references describe crepe paper specifically as a material for irregular shapes and surfaces inside a transformer. Typical crepe paper products are offered in different thicknesses and elongation levels depending on the application.

So while DDP is designed to bond winding layers, crepe paper is designed to adapt to geometry.

3. Quick Comparison: DDP vs Crepe Paper

This is the core reason buyers should not treat the two papers as substitutes. One is selected for bonded winding structure. The other is selected for flexible insulation fit.

4. When Should You Use Diamond Dotted Paper?

Diamond dotted paper is usually the better choice when the transformer winding needs:

interlayer insulation

stable bonded winding layers

improved mechanical integrity in the coil

better resistance to layer displacement

a more integrated winding structure after curing

This is why DDP is widely used in winding constructions where bonding is important, especially in transformer coils that benefit from stronger internal stability.

A practical way to think about it is this:

If the winding needs to stay together as a more stable unit after heating and drying, DDP is usually the right direction.

5. When Should You Use Crepe Paper?

Crepe paper is the better choice when the transformer part is difficult to insulate with flat paper.

Typical situations include:

• wrapping leads

• covering corners and edges

• insulating curved conductors

• local insulation on uneven parts

• any position where flexibility matters more than bonding

A simple rule is:

If the insulation must stretch or follow an irregular shape, crepe paper is usually the better choice.

6. DDP vs Crepe Paper in Transformer Windings

This is where buyers often need the clearest answer.

For winding layers

If the material is going between layers and you want insulation plus bonding, use diamond dotted paper. Its purpose is to help hold layers together after thermal processing.

For local wrapping around winding parts

If the material is needed around leads, bends, corners or irregular winding areas, use crepe paper. Its purpose is flexible insulation coverage, not layer bonding.

So the real comparison is not:

Which paper is better for transformers?

The better question is:

Which paper is better for this part of the transformer?

7. Thickness and Material Structure

Thickness alone does not tell the full story, but it does help explain the difference.

Public product information shows:

• Diamond dotted paper is commonly offered around 0.08 mm to 0.50 mm

• Crepe paper is commonly offered around 0.05 mm to 0.13 mm, with different elongation levels depending on the application

That does not mean one is always thicker than the other in every case. The more important point is that the structure is different:

• DDP = base insulation paper + resin dots

• Crepe paper = creped cellulose structure for stretch and conformity

So if you are choosing only by thickness, you may miss the most important difference, which is function.

8. Common Buyer Mistakes

Mistake 1: Comparing only by product name

The name does not explain the function. The application does.

Mistake 2: Treating all transformer papers as substitutes

DDP and crepe paper are both transformer insulation papers, but they serve different jobs.

Mistake 3: Choosing only by price

A lower paper cost does not help if the material cannot perform the required function.

Mistake 4: Ignoring the production process

DDP is closely related to winding drying and curing behavior. Crepe paper is closely related to wrapping and fitting behavior. 

9. How to Choose the Right One

Use this simple decision logic:

Choose Diamond Dotted Paper if:

the transformer winding needs layer bonding

winding stability is important

coil integrity after curing matters

the application is interlayer winding insulation

Choose Crepe Paper if:

the insulation area is curved, uneven or irregular

leads or corners must be wrapped

flexibility matters more than bonding

local fit is more important than winding adhesion

In simple terms:

Diamond dotted paper is for bonded winding structure.

Crepe paper is for flexible wrapping and local insulation.

FAQ

Q1: What is diamond dotted paper used for in transformers?

A: Diamond dotted paper is mainly used for interlayer insulation where bonding and winding stability are required. It helps strengthen the winding structure during thermal processing.

Q2:What is crepe paper used for in transformers?

A:Crepe paper is mainly used for irregular shapes, leads, corners and curved surfaces where flat insulation paper cannot fit properly.

Q3:Does DDP improve oil impregnation?

A: Yes, one reason DDP is designed with dotted resin rather than full coating is to support drying and oil impregnation through the open channels.

CTA

Looking for reliable transformer insulation paper for winding insulation and local wrapping applications?

We supply a full range of transformer insulation materials, including:

• diamond dotted paper

• crepe paper

• kraft insulation paper

• thermally upgraded paper

• transformer pressboard

Contact us for product details, thickness options and bulk quotation support.