Paper, defined.

The tallest standard flute profile (~4.7 mm high, 33 flutes per 30 cm). Gives the best cushioning and stacking strength for heavy, fragile goods.

A wax-like internal sizing agent that reacts with cellulose to create a water-repellent fiber surface. Works at neutral pH.

A regulatory parameter measuring chlorinated organic compounds in pulp mill effluent. Tracked to monitor ECF bleaching emissions.

A medium flute profile (~2.5 mm high, 49 flutes per 30 cm). Common for retail-ready boxes and die-cut displays.

A compressed, wired bundle of recovered paper or market pulp, the standard shipping unit for bulk paper raw materials.

A thin functional coating that gives paper resistance to grease, moisture, or oxygen. A key enabler of paper-for-plastic replacement.

The mass of a standard number of sheets at a reference size, used in North America alongside grammage (g/m²).

Chemical removal of residual lignin from chemical pulp to produce white pulp. ECF (chlorine dioxide) and TCF (oxygen, ozone, peroxide) are the two major systems.

Two different measurements, two different standards, routinely conflated on datasheets. Here is what each number actually means.

The volume per unit mass of a paper, calculated as caliper divided by grammage, reported in cm³/g.

The hydraulic pressure that punctures a sheet. Why corrugated liner grades are specified by burst index, and what the numbers actually mean.

The most common shipping-box flute (~3.6 mm high, 39 flutes per 30 cm). The default choice for general corrugated boxes.

A finishing step where the sheet passes through pressurized roll nips to smooth the surface and control caliper.

Micrometers, microns, and points. Why two papers at the same GSM can have completely different thickness, and why it matters.

The compressive strength test for corrugating medium. How the concora fluter works, what CMT values mean, and why flat crush resistance is the right metric for fluting grades.

The mass of water absorbed by a paper in 60 seconds (Cobb60) per square metre, a standard water resistance measurement.

A sandwich of paper liners bonded to a fluted medium, used to make shipping boxes. Single, double, or triple wall configurations are standard.

The machine that forms corrugated board by fluting the medium, applying starch adhesive, and bonding it to the liners in a continuous process.

A tissue-making step where the dry sheet is scraped off the Yankee dryer with a doctor blade, creating fine longitudinal folds that produce softness and stretch.

The total producible width of a paper machine. Also a term for the uneven edge on handmade or mould-made paper.

Pulp made from recovered printed paper where ink has been removed, used in newsprint, tissue, and graphic grades.

The part of the paper machine where the sheet dries to final moisture by contact with steam-heated cylinders.

A microflute profile (~1.5 mm high, 95 flutes per 30 cm). Used for small retail boxes, gift boxes, and printable packaging.

ISO 3037 / TAPPI T811. The compression test for assembled corrugated board, not the individual liners or medium. Why ECT predicts box compression strength and what typical values look like.

A standardized four-digit code system identifying corrugated box styles, published by FEFCO (European Federation of Corrugated Board Manufacturers).

The definitive reference for corrugated flute dimensions. A through N: what each profile is, how thick it is, how many flutes per metre, and what it's actually used for.

The wavy inner layer of corrugated board. What fluting paper is, how it's made on a corrugator, and why the wave geometry, not the fibre density, provides structural strength.

The traditional single-wire paper machine design where stock drains through a moving mesh. Invented 1803, still dominant for many grades.

A measure of how readily a pulp dewaters, reflecting the degree of refining. Lower freeness means more refined, slower-draining pulp.

A paper machine forming section that sandwiches the stock between two converging wires, giving two-sided drainage and uniform formation at high speed.

A paper filler and coating pigment made by grinding limestone. The most-used inorganic additive in paper worldwide.

The fraction of incident light a paper reflects at a fixed angle, measured at 20°, 60°, or 75° in a gloss meter.

The international unit for paper weight, measured in grams per square metre (g/m²). Also called GSM.

The single most important number on any paper spec sheet. What it measures, what it isn't, how to read it.

Pulp from broadleaf trees (eucalyptus, birch, aspen) with short fibers (0.8 to 1.2 mm) that provide smoothness and opacity.

The component of a paper machine that deposits stock onto the forming wire at controlled consistency, flow, and width.

International commercial trade terms defining who pays shipping, insurance, and customs costs in a paper trade deal.

A layered aluminosilicate clay used as a paper coating pigment, particularly for glossy and gloss-control coated papers.

Chemical pulp produced by cooking wood chips with sodium hydroxide and sodium sulfide. The dominant pulp process globally.

A polymer dispersion that binds coating pigments to each other and to the paper surface. Styrene-butadiene is the dominant chemistry.

The natural polymer that bonds wood cells together. Removed in chemical pulping, retained in mechanical pulping.

High-yield pulp made by mechanically separating wood fibers, retaining lignin. Used in newsprint and magazine papers.

A hydraulic test that measures the pressure required to rupture a paper sample, reported in kPa.

Semichemical pulp made from hardwood with a mild sulfite pretreatment followed by mechanical refining. The standard furnish for virgin fluting.

A chemical that absorbs UV light and re-emits visible blue light, making paper appear whiter and brighter than physics would allow without it.

Recovered corrugated boxes, the primary feedstock for recycled containerboard (testliner and recycled fluting).

How much light passes through the sheet. Why show-through ruins thin paper. How it is measured and what ranges to expect.

A synthesized calcium carbonate, chemically identical to GCC but with controlled particle size and shape. Used where optical performance matters.

How easily air passes through a paper, measured as time for a fixed air volume (Gurley) or as flow rate at fixed pressure (Bendtsen).

The part of the paper machine after forming where water is squeezed from the wet sheet by passing it through pressurized roll nips with felts.

A large cylinder of paper wound onto a core at the end of the paper machine. The base unit of production and bulk shipment for most grades.

A stock preparation step where pulp passes between rotating discs with bars, mechanically working the fibers to increase bonding and strength.

ISO 12192 / TAPPI T822. A paperboard strip bent into a ring, then edge-compressed. Why RCT matters for both liner and medium, and how it relates to SCT as the industry convergence point.

The standard four-flap shipping box style: all four outer flaps meet at the centre when closed. The most produced box style globally.

A test of compressive strength over a very short span (0.7 mm), now the preferred predictor of corrugated box compression strength.

The treatment that makes paper resistant to water and aqueous inks. Internal sizing is added to the furnish; surface sizing is applied to the dry sheet.

The surface regularity of a paper, measured by air leak under a pressurized head (Parker Print Surf, Bendtsen).

Pulp from coniferous trees (pine, spruce, fir) with long fibers (2 to 4 mm) that provide strength and tear resistance.

A polysaccharide used as internal strength additive, surface sizing polymer, and adhesive in coatings and corrugated bonding.

Resistance to bending, measured by Taber stiffness tester or L&W 5° bending tester, reported in mN·m or Taber units.

The energy a paper absorbs before it breaks under tension, a key measure of toughness in sack kraft and other stretch-critical grades.

The force required to propagate a tear in paper, measured by Elmendorf pendulum tester in mN.

The fraction of a paper's dry strength retained when saturated with water, critical for food-contact and labeling papers.

A measurement of how white a paper appears, taking into account fluorescence from optical brighteners, distinct from brightness.