Pressboard vs Transformerboard: What Is the Difference?

Published 27 Aug 2026Updated 27 Aug 20264 min readBeginnerInsulation

Quick answer — They are closely related but the terms are not fully interchangeable. "Transformerboard" is the general term for electrical insulation board made of 100 % unbleached sulphate (kraft) pulp. "Pressboard" is a higher-density, highly compressed form of that board, calendered after pressing, used for barriers, supports, spacers and other structural insulation in oil-filled transformers.

Contents

Manufacture
Grades
Selection

What is the difference between pressboard and transformerboard?

Manufacture

Both start from pure kraft pulp. Pressboard is compressed and calendered to raise density, strength and oil resistance, giving a uniform, high-density board with good dielectric and mechanical properties.

Grades

Board is offered in several grades differing in density and finish, chosen for whether it is used as a lead barrier, a spacer, a winding support or a major insulation structure.

Selection

Density and thickness are selected for the dielectric stress and mechanical duty, and the board must be compatible with the insulating fluid (mineral oil or ester) and free of contaminants and conductive particles.

References & standards

IEC 60076-1
IEEE C57.12.00

Book series Academy

Related manufacturers

Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp

Related components

Insulation materials

Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.

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