Linerboard — The Flat Outer Layers of Corrugated Board

What Is Linerboard?

Linerboard is the flat paper sheet that forms the outer faces of corrugated fiberboard. Every corrugated structure has at least one linerboard face bonded to the tips of the fluted medium with adhesive. In a standard single wall box, there are two linerboard layers — one inside and one outside — with the fluted medium between them.

Linerboard serves multiple critical functions: it provides the smooth surface for printing and branding, resists puncture and abrasion, distributes loads evenly across the flute structure, and protects the fluted medium from direct contact with the environment.

Types of Linerboard

The corrugated industry uses several categories of linerboard, each suited to different performance and appearance requirements:

• Kraft linerboard: Made from virgin wood pulp, this is the strongest option. Its natural brown color is the default appearance of most shipping boxes.
• Recycled linerboard (test liner): Manufactured from recovered paper fibers. Available in similar basis weights as kraft, with slightly different strength properties.
• Mottled white linerboard: Features a white-coated surface over a brown or recycled base for a premium outer appearance.
• Bleached white linerboard: Fully white throughout the sheet, used when maximum visual appeal or food-contact whiteness is required.
• Pre-printed linerboard: Linerboard that is printed before corrugating, enabling high-quality graphics on large-volume runs.

Linerboard Grades and Basis Weight

Linerboard is specified by its basis weight — the weight in pounds per 1,000 square feet. Common basis weights include 26 lb, 33 lb, 38 lb, 42 lb, 47 lb, 56 lb, 69 lb, and 90 lb. The basis weight of the linerboard, combined with the medium weight and flute profile, determines the overall board grade and performance of the finished packaging.

Heavier linerboard increases puncture resistance, stiffness, and compression strength but also adds cost and shipping weight. The engineering team at President Container specifies the lightest linerboard that meets performance requirements to optimize the cost-to-protection ratio.

Inner vs. Outer Liner

In many corrugated constructions, the inner and outer linerboard are not identical. The outer liner (which faces the shipping environment) is often a heavier or higher-quality grade to resist scuffing, moisture, and handling damage. The inner liner (which contacts the product) may use a lighter grade or a specialty surface for product protection.

This mix-and-match approach is common in cost-optimized packaging. For retail displays and shelf-ready packaging, the outer liner might be a mottled white or bleached white for premium print quality, while the inner liner remains standard brown kraft.

Linerboard and Print Quality

The linerboard surface is where all printing takes place on a corrugated box. Smoother, whiter linerboard produces sharper graphics with better color reproduction. This is particularly important for shelf-ready packaging and point-of-purchase displays where visual impact drives purchasing decisions. Finer flute profiles like E-flute and F-flute also improve print quality by creating a smoother underlying surface for the linerboard.