Kraftliner

What is kraftliner paper?

Kraftliner is a paperboard used on the outside faces of corrugated boxes. It is produced from virgin softwood kraft pulp, which gives it the long fibers needed for high strength. The name comes from the kraft process, the alkaline cooking method that liberates cellulose from wood without breaking it down.

The defining property is burst strength. Kraftliner measured on a Mullen tester typically sits between 300 and 900 kPa depending on grammage. That matters because kraftliner carries the load. Inside the corrugated sandwich, fluting does the shock absorption and testliner or an inner kraftliner ply handles the secondary bonding. The outside face is what stacks, what survives the forklift drop, and what gets printed on.

Per CEPI's 2024 market data, virgin containerboard accounts for roughly 30% of European containerboard output, with kraftliner the largest subset. CEPI Key Statistics 2024.

How is kraftliner made?

Production starts at the digester where softwood chips cook with sodium hydroxide and sodium sulfide at around 170°C. The cook breaks lignin bonds but keeps fiber length largely intact. Pulp is washed, screened, and sent to stock preparation. From there it hits a Fourdrinier or hybrid former, presses, and a long dryer section. Some mills add a size press for dimensional stability. Final grammage is controlled by headbox flow and wire speed.

Bleaching is rare. Most kraftliner stays brown, which is why box suppliers often call it brown top. A minority of mills produce a two-ply kraftliner where the top ply carries a small white fraction for print contrast.

What grammages does kraftliner come in?

The commercially relevant range is 100 to 250 g/m². The most traded grammages for export packaging are 135 and 175 g/m². Grammages below 115 g/m² are usually lightweight kraftliner intended for e-commerce boxes where box weight matters. Above 200 g/m² the product edges into heavyweight containerboard for export and long-haul applications.

Browse all kraftliner grade specifications in the World Paper Index.

Kraftliner vs testliner: what is the difference?

Kraftliner uses virgin softwood pulp. Testliner uses recycled fiber, often recovered from old corrugated containers. Kraftliner outperforms testliner on burst strength, ring crush, and moisture resistance but costs more. A typical rule in box design: use kraftliner where the box crosses borders, holds food, or stacks in humid conditions. Use testliner where the box has a short working life and cost matters more than worst-case strength.

WPI's grade-vs-grade comparison index runs through kraftliner and testliner spec by spec.

Who are the main kraftliner producers?

Scandinavia dominates. Sweden and Finland together produce more kraftliner than the rest of Europe combined, driven by cheap softwood, integrated mills, and long export history. Mondi Svenska Skog, BillerudKorsnäs, Stora Enso, and Smurfit Kappa Nettingsdorf are the names that turn up in most purchasing specs. Outside Europe, Georgia-Pacific and International Paper anchor North American supply. Klabin, Suzano, and CMPC supply the Southern Cone.

Brazil is the fastest growing supplier. Per RISI's 2024 annual outlook, South American kraftliner capacity grew 8% year on year as Klabin's Puma II machine came online. Browse kraftliner mills by country.

What certifications apply to kraftliner?

FSC and PEFC dominate. Both certify chain-of-custody back to the forest, which matters for EU customers under the Deforestation Regulation and for US customers specifying sustainably sourced fiber. Food-contact kraftliner carries additional certifications: BfR XXXVI in Germany, FDA 21 CFR 176.170 in the US, and ISEGA in certain European markets. See the WPI certifications index for the full list.

Most major Scandinavian kraftliner mills hold both FSC and PEFC concurrently. That dual coverage is less common in South America and Asia, where FSC is the more widely recognized label.

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