Linerboard
Linerboard is the flat, smooth paper layer bonded to either side of a corrugated medium to form a corrugated board. It provides the strength, printability, and outer surface of a cardboard box.
A corrugated board is a sandwich: two layers of linerboard with a fluted medium glued between them. The linerboard carries the surface forces — burst strength, edge crush, print quality — while the medium handles cushioning and stack compression. Heavier or higher-grade linerboard makes a stronger box.
Linerboard is sold by basis weight, in pounds per 1,000 square feet (a different parent area than fine papers — see basis weight). Common North American grades include 26-lb, 33-lb, 42-lb, and 56-lb, with 42 being the workhorse. Mills also offer mottled white, fully bleached, and recycled linerboards alongside the standard kraft-brown product.
Inside a single shipment manifest, the same mill often ships several linerboard grades to the same customer, and the grade codes look superficially similar. This is where careless field extraction goes wrong: dropping the basis-weight digits or transposing a grade family can move a roll to the wrong inventory bucket.
Related terms
- Basis weightBasis weight is the standard measure of paper weight in the U.S., expressed in pounds per 3,000 square feet of a grade's parent sheet. Elsewhere it is reported as grams per square metre (gsm).
- Kraft paperKraft paper is strong, typically brown paper produced by the kraft pulping process — a chemical method that preserves long cellulose fibres. It is the dominant fibre source for linerboard, shipping sacks, and packaging.
- Corrugating mediumCorrugating medium is the fluted middle layer of a corrugated board, sandwiched between two layers of linerboard. The flutes provide compressive cushioning and stack strength; the medium itself does not need the surface qualities of a liner.
- FlutingFluting refers to the wave pattern formed in corrugating medium between two layers of linerboard. The flute profile — A, B, C, E, and F being the common standards — determines compression strength, cushioning, and printability.
- Edge crush test (ECT)ECT measures the edgewise compressive strength of a corrugated board, reported in pounds per inch or kN/m. It is the standard predictor of stacking strength and has largely replaced burst strength as the spec for box certification.
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