Electrical transformers rely on multiple types of insulation materials to manage heat, voltage, and mechanical stability. Two of the most widely used solid insulation materials are pressboard and transformerboard. Though they are often confused, each serves a distinct role in transformer construction.
1.What Are Pressboard and Transformerboard?
Pressboard is a cellulose-based dry-pressed insulation board, manufactured from high-purity kraft pulp. It is typically used in winding structures and between transformer layers for insulation and oil flow control.
Transformerboard is also made of cellulose but produced using a wet-laid process, which results in a denser, more compact, and mechanically stronger material. It is commonly used for rigid insulation parts like clamping rings, support frames, and end barriers.
Both materials comply with international electrical standards—pressboard with IEC 60641, transformerboard with IEC 60763.
2.Comparison Table: Key Differences
| Feature | Pressboard | Transformerboard |
|---|---|---|
| Production Method | Dry-pressed kraft pulp | Wet-laid insulation board |
| Thickness Range | 0.3 – 8.0 mm | 1.0 – 100 mm |
| Use Cases | Coils, ducts, cylinder layers | Clamping, frames, end rings |
| Mechanical Strength | Moderate | High |
| Oil Absorption | Excellent | Moderate |
| Standards | IEC 60641 | IEC 60763 |
3.When to Use Pressboard vs Transformerboard?
Choose pressboard when you need:
- Winding layer insulation
- Coil duct spacers
- Cylindrical barriers in oil-filled transformers
Choose transformerboard when you need:
- High-rigidity structural support
- Machined clamping blocks and end barriers
- Material performance under mechanical stress or HV zones
➡️ Use-case depends on function: layer separation vs structural integrity.
4.Material Properties Overview
While both are cellulose insulation materials, their structure and behavior differ:
| Property | Pressboard | Transformerboard |
| Surface Texture | Smooth, flexible | Hard, rigid |
| CNC Process Compatibility | Excellent for cutting, punching | Excellent for milling and drilling |
| Dielectric Performance | Excellent in oil (≥60 kV) | Good under compression |
| Density | ~1.0 – 1.2 g/cm³ | ~1.2 – 1.3 g/cm³ |
5.Choosing the Right Material for Your Project
Before sourcing transformer insulation boards, consider:
📌 Voltage Class – Higher voltages require rigid support, favoring transformerboard.
📌 Design Geometry – Tight coils and ducts benefit from flexible pressboard.
📌 Processing Needs – Ask your transformer pressboard manufacturer if CNC pre-shaped parts are available.
Always request:
- SGS-tested results or third-party validation
- IEC 60641 / IEC 60763 compliance certificates
- Thickness and tolerance specs by batch
➡️ These steps help ensure you choose a safe, stable, and high-performing insulation solution.
5.Conclusion & CTA
Both pressboard and transformerboard are essential in transformer insulation—but their use cases are different. Pressboard is perfect for layering and duct flow. Transformerboard shines in mechanical reinforcement and large structural applications.
👉 Contact us for technical support, datasheets, or sourcing transformer insulation boards tailored to your project.
✅ Response within 24 hours. Pre-cut shapes and samples available on request.
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