What is fluting paper?
Fluting, also called corrugating medium or the medium, is the wavy middle ply of corrugated board. It is bonded between two liners (kraftliner or testliner) to form the corrugated sandwich used in boxes. The wave geometry is what gives corrugated board its stiffness, compression strength, and shock absorption properties. Flat paper cannot do any of those things.
Fluting grammage runs 80 to 200 g/m², with 115 and 140 g/m² the most traded weights. The fluting is typically the lightest ply in the corrugated sandwich: a 140 g/m² fluting between two 175 g/m² kraftliners creates a strong export box.
How is fluting made?
Two production routes dominate. Semichemical fluting (NSSC, neutral sulfite semichemical) cooks hardwood chips (usually birch or oak) in a mild chemical bath, producing a high-yield pulp with intermediate strength. NSSC fluting has better stiffness and moisture performance than recycled fluting. Recycled fluting is made entirely from recovered OCC (old corrugated containers). It uses the same equipment as testliner production, often in the same mill.
The paper machine is a conventional Fourdrinier with relatively few press nips (because fluting does not need a smooth surface). Machine speeds run 800 to 1200 m/min, similar to testliner.
What grammages does fluting come in?
Most commercial fluting is in the 90 to 180 g/m² range. 115 and 140 g/m² are the most traded grades. Lightweight fluting at 80 to 90 g/m² serves e-commerce boxes where package weight matters. Heavyweight fluting at 180 to 200 g/m² goes into export and heavy-duty boxes.
The flute profile (A, B, C, E, F, N) determines the wave pitch and the height. C flute is the most common for shipping boxes. E and F flutes are thinner, used for retail-ready packaging and smaller cartons. N flute is microflute, used where a box needs a premium print surface.
Why does CMT matter for fluting?
CMT (concora medium test) measures the crush resistance of fluting in a laboratory. It is the single most important fluting spec because it directly correlates with the stacking strength of the finished corrugated box. Higher CMT means the box can hold more weight stacked on top. A 140 g/m² semichemical fluting typically has a CMT of 270 to 320 N. A 140 g/m² recycled fluting typically runs 200 to 260 N, roughly 20% weaker per gram.
See the CMT glossary entry for the full test method and interpretation.
Who are the main fluting producers?
Semichemical fluting is produced in integrated pulp-and-paper mills with access to hardwood. Mondi, BillerudKorsnäs, Stora Enso, and Sappi Gratkorn operate the main European semichemical mills. In North America, Georgia-Pacific, International Paper, and Packaging Corporation of America run large semichemical fluting capacity.
Recycled fluting mills are far more numerous because they need only a recycled paper source, not forest access. Most European testliner mills also produce recycled fluting on the same machines. Asia's recycled fluting capacity expanded sharply after 2018, led by Nine Dragons, Lee and Man, and Shandong Chenming.
What certifications apply to fluting?
FSC and PEFC are the relevant forestry labels. Food-contact fluting carries BfR XXXVI (DE) and FDA 21 CFR 176.170 (US) when the corrugated box contacts food. For the recycled stream, FSC Recycled and PEFC Recycled apply. Recyclability is covered by the 4evergreen protocol in Europe.
Frequently asked questions
What is the difference between semichemical and recycled fluting?
Semichemical fluting (NSSC) uses virgin hardwood pulp and delivers higher CMT (crush strength) per gram. Recycled fluting uses recovered OCC and delivers lower CMT at lower cost. Semichemical is preferred for export and heavy-duty boxes; recycled is standard for domestic distribution.
What GSM is standard fluting?
115 and 140 g/m² are the most traded fluting grammages. Lighter 90 to 100 g/m² grades serve e-commerce and retail-ready packaging. Heavier 160 to 180 g/m² grades go into heavy-duty export boxes.
What is CMT and why does it matter?
CMT (concora medium test) measures the crush resistance of fluting in a lab. It correlates with the stacking strength of the finished corrugated box. Higher CMT means the box can hold more weight stacked on top. Semichemical fluting typically has 20 to 30% higher CMT per gram than recycled fluting.
What flute profiles exist?
A flute (5 mm) is the tallest and most common for heavy-duty boxes. C flute (4 mm) is the general-purpose default. B flute (2.5 mm) is thinner, used for display boxes. E (1.5 mm) and F (0.8 mm) flutes serve retail-ready packaging. N flute (below 0.8 mm) is microflute for premium print.
Is fluting cheaper than kraftliner?
Yes, fluting is typically 10 to 20% cheaper per tonne than kraftliner. Recycled fluting is cheaper still, roughly 25 to 35% below kraftliner. The price differential reflects the different furnish and the less demanding surface requirements.
Can recycled fluting replace semichemical fluting?
In many applications yes, but not all. Semichemical is still preferred for heavy export boxes, humid storage, and food-safe multilayer packaging where moisture resistance matters. Recycled fluting dominates domestic distribution boxes where its lower cost outweighs its lower CMT.