Kraft paper
Kraft 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.
The kraft process treats wood chips with sodium hydroxide and sodium sulphide to dissolve the lignin that holds wood fibres together, leaving the cellulose fibres intact and long. 'Kraft' is German for strength, which is what the process produces: paper that resists tearing and bursting better than mechanical-pulp paper of the same weight.
Kraft pulp is the input to a family of paper products. Unbleached kraft is the familiar brown linerboard, kraft paper bag, and shipping sack. Bleached kraft — usually noted as BK, B/W, or 'mottled' on documents — is the food-grade and printing-grade product. Both share the same underlying fibre length and strength characteristics.
On a manifest, 'kraft' rarely tells you what you actually received. It is a fibre source, not a grade specification. Pair it with basis weight, treatment (bleached vs unbleached), and product form (roll, sheet, bag) to identify what was actually shipped.
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.
- Mechanical pulpMechanical pulp is pulp produced by grinding or refining wood physically rather than dissolving the lignin with chemicals. It retains nearly all of the wood's mass — high yield, low cost — at the price of shorter fibres and remaining lignin.
- Bleached paperBleached paper is paper that has been chemically processed after pulping to remove the brown colour of residual lignin and produce a white surface. Modern bleaching is ECF (elemental chlorine free) or TCF (totally chlorine free).
- 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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