Corrugating medium
Corrugating 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.
Medium is typically a lower basis weight than the liner around it — 26, 30, or 33 lb per 1,000 sq ft is common — and is often made from semi-chemical pulp or recovered fibre because it never faces the outside of the box.
A corrugated board is a sandwich: outer liner, fluted medium, inner liner, bonded with starch adhesive. The medium is shaped into the flutes by a corrugator's flute-forming rolls just before bonding.
Mills sell medium as roll paper, the same way they sell linerboard. The two often ship together — receivers see a truck with several rolls of liner and several rolls of medium destined for a corrugator plant downstream.
Related terms
- LinerboardLinerboard 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.
- 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.
- ContainerboardContainerboard is the umbrella term for paper products used to make corrugated boxes: specifically linerboard and corrugating medium. North American containerboard production is one of the largest paper categories by tonnage.
- 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).
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