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Sample boxes What is a corrugated liner?
The term “liner” refers to the smooth sheets of paper on the outer and inner surfaces of corrugated board. These liners are bonded to the corrugated medium in between to form a sturdy composite. The type of liner used is a key factor in determining the stability, appearance, and surface quality/printability of the corrugated board.
Types of liners
The most common types of liners differ primarily in terms of composition and performance level. In terms of composition, a distinction is made between virgin and recycled fibers.
- Kraftliner: high-quality linerboard containing more than 50% virgin fiber (kraft pulp) and offering excellent strength. Kraftliner is typically available in white, mottled (slightly speckled), or white-coated finishes.
- Testliner: is typically made from 100% recycled fiber and is classified into four quality grades. Grade 1 is the highest quality grade. Testliner is available in uncoated and coated varieties, as well as in white and coated versions.
- Kraft Top Liner: is a recycled fiber liner with a top layer consisting mainly of kraft fibers; it is used as a compromise between testliner and kraftliner.
Liner weights
In practice, liners are selected based on basis weight (g/m²) depending on the specific application. Generally, the higher the basis weight, the higher parameters such as stiffness, puncture resistance, and the overall stability of the finished corrugated board surface—though this also increases material usage and costs. Typical liner basis weights range from approximately 125 to 300 g/m².
How do I choose the right liner?
The selection of the right liner typically depends on:
- Load profile (e.g., stacking, puncture resistance, edge protection)
- Printability/Appearance (brown vs. white/coated)
- Moisture requirements (e.g., “glued”/Cobb value, depending on the application)
- Costs & Sustainability Goals (Fresh or Recycled Fiber)
In most cases, kraft liner is used to ensure maximum stability. Testliner, on the other hand, is the more economical standard choice for many types of corrugated board under normal loads, while Kraft Top Liner often offers the ideal compromise. White-coated liners are particularly well-suited for producing a high-quality print image.
