Corrugated Industry Glossary

The original and largest standard flute profile, with approximately 33 flutes per linear foot and a flute height of about 3/16 inch (4.8 mm). A-flute provides excellent cushioning and stacking strength, making it suitable for fragile items and heavy-duty shipping containers. It is thicker than B, C, E, or F flutes.

The bonding agent used to attach linerboard to the corrugated medium. Most corrugated board is manufactured with starch-based adhesive (typically cornstarch or wheat starch), which is inexpensive, fast-setting, and does not interfere with recycling. Adhesive formulation and application are critical to board quality, affecting pin adhesion, warp, and running speed on the corrugator.

A flute profile with approximately 47 flutes per linear foot and a height of about 1/10 inch (2.5 mm). B-flute offers good flat crush resistance and a smooth printing surface, making it popular for die-cut boxes, displays, and canned goods packaging. It is thinner than A- and C-flute.

The weight of paper expressed in pounds per 1,000 square feet (MSF) or grams per square meter (GSM). Basis weight is a key specification for linerboard and corrugating medium, directly affecting the strength and cost of finished corrugated board. Common linerboard basis weights range from 26 lb to 90 lb per MSF.

A test that measures the maximum compressive load a finished corrugated box can withstand before crushing. BCT is expressed in pounds of force and is the primary indicator of a box's stacking strength. It is influenced by board grade, flute type, box dimensions, and moisture content. McKee's formula is commonly used to estimate BCT from ECT values.

Flat, scored, and slotted corrugated sheets that have been cut to size and are ready to be folded and assembled into boxes. Blanks are the output of the converting process (slitting, scoring, and cutting on the corrugator or a separate converting machine) and may be shipped flat to the end user for on-site erection.

A designation that specifies the combination of liner and medium weights used to construct corrugated board. For example, "200#/ECT-32" indicates a board rated for 200 pounds per square inch bursting strength or 32 pounds per linear inch edge crush. Board grade determines the strength, weight, and cost of corrugated packaging.

The round stamp printed on the bottom flap of most corrugated boxes, containing key specifications: the board construction (single, double, or triple wall), ECT or Mullen rating, box size, weight limits, and the manufacturer's name and facility code. The certificate serves as a quality guarantee and is defined by Rule 41 (rail) and Item 222 (motor freight) carrier classification rules.

The pressure required to puncture the face of corrugated board, measured in pounds per square inch (psi) using a Mullen tester. Historically the primary strength metric for corrugated boxes, bursting strength has been largely supplanted by ECT for most shipping applications. Common ratings include 175#, 200#, 275#, and 350#.

The most widely used flute profile in North America, with approximately 39 flutes per linear foot and a height of about 9/64 inch (3.6 mm). C-flute offers a balance between cushioning, stacking strength, and printing surface quality. It is the default choice for most regular slotted container (RSC) shipping boxes.

The thickness of paperboard or corrugated board, measured in thousandths of an inch (points or mils). Caliper is critical for determining board rigidity, cushioning, and compatibility with converting equipment. A typical C-flute single wall board measures approximately 150-160 mils.

The broad term for paperboard grades used to manufacture corrugated board, encompassing both linerboard (the flat facing sheets) and corrugating medium (the fluted inner layer). Containerboard is produced from virgin kraft fiber, recycled fiber, or a blend of both. The U.S. produces approximately 35 million tons of containerboard annually.

A company that purchases corrugated sheets or rolls from an integrated mill or sheet feeder and converts them into finished boxes and packaging products. Converters (also called independent sheet plants) perform printing, die-cutting, folding, and gluing operations. They typically serve regional markets and compete with the converting operations of vertically integrated producers.

The paperboard sheet that is formed into the fluted (wavy) layer between the liners in corrugated board. Medium is typically made from semi-chemical hardwood pulp or recycled fiber and commonly ranges from 23 lb to 40 lb basis weight. The medium is the structural core that gives corrugated board its strength-to-weight ratio.

A flat piece of corrugated board cut to a specific size, as opposed to a finished box. Corrugated sheets are sold by integrated mills and independent sheet feeders to smaller converters who do not operate their own corrugators. Sheets can be single wall, double wall, or triple wall in any flute combination.

The large machine (often 300+ feet long) that combines linerboard and corrugating medium into finished corrugated board. The corrugator heats, moistens, and flutes the medium, then glues it to liner sheets on one or both sides. Modern corrugators run at speeds exceeding 1,000 feet per minute and represent the single largest capital investment in a box plant.

A box or packaging component that is cut to a specific shape using a steel-rule die, as opposed to being scored and slotted on a flexo-folder-gluer. Die-cutting allows for complex shapes, hand holes, locking tabs, and precise tolerances. Die-cut boxes are more expensive to tool than RSCs but offer greater design flexibility.

Corrugated board constructed with two fluted layers and three liner sheets, creating a five-ply structure. Double wall provides significantly greater stacking strength and puncture resistance than single wall. Common flute combinations include BC (B-flute + C-flute) and AC. Used for heavy products, export shipping, and applications requiring high box compression.

A fine flute profile with approximately 90 flutes per linear foot and a height of about 1/16 inch (1.6 mm). E-flute provides a smooth, high-quality printing surface and is commonly used for retail packaging, pizza boxes, folding carton replacements, and primary packaging where shelf appearance matters.

A test that measures the edgewise compressive strength of corrugated board, expressed in pounds per linear inch. ECT is the primary predictor of a box's stacking strength and has become the dominant specification method in North America. Common ECT ratings include 23, 29, 32, 40, 44, 48, and 71 ECT. Higher ECT values indicate greater compression resistance.

The smallest standard flute profile, with approximately 125 flutes per linear foot and a height of about 1/32 inch (0.8 mm). F-flute competes directly with folding cartons and is used for cosmetics packaging, small electronics, fast food containers, and other applications requiring thin board with excellent printability.

The European Federation of Corrugated Board Manufacturers. FEFCO maintains the internationally recognized FEFCO-ESBO code system, a standardized catalog of corrugated box and packaging designs identified by numeric codes (e.g., FEFCO 0201 is the standard RSC). The code system is used worldwide as a common language for box design specifications.

The extensions of a box's side panels that fold to close the top and bottom of the box. Major flaps (on the length panels) typically meet at the center when folded, while minor flaps (on the width panels) are shorter. Flap configuration affects box closure, stacking strength, and material usage.

A test measuring the resistance of the corrugated medium's fluted structure to a flat compressive force, expressed in pounds per square inch. Flat crush resistance indicates how well a board will resist damage from pressure applied to its face, such as during printing, palletizing, or rough handling. Low flat crush values suggest damaged or poorly formed fluting.

The dominant printing method in the corrugated industry, using flexible photopolymer printing plates and fast-drying water-based inks. Flexo printing can be done directly on corrugated board (post-print) or on linerboard before it is laminated to the corrugated structure (pre-print). Post-print flexo is the most cost-effective method for high-volume box printing.

The wave-shaped arches formed in the corrugating medium that are sandwiched between flat linerboard sheets. Flutes are the structural element that gives corrugated board its rigidity, cushioning, and compression strength. Standard flute profiles, from largest to smallest, are A, C, B, E, and F.

A box style where the major flaps on the top and bottom fully overlap each other when closed, providing extra stacking strength and bottom support compared to a standard RSC. FOL boxes (FEFCO 0202) use more material but are preferred for heavy products or items that need a reinforced base.

A large, heavy-duty corrugated box typically sized to fit on a standard pallet (approximately 48" x 40" x 36"), used for bulk shipping and storage of loose or granular materials. Gaylord boxes are usually triple wall or heavy double wall construction. The term is widely used in industrial packaging and recycling, and "gaylord" has become a generic industry name for any pallet-sized bulk box.

A box with one set of flaps (typically the top) removed, creating a tray-like container with an open top. HSCs are commonly used with a separate lid or as stackable trays in agricultural produce, retail displays, and industrial storage. They are sometimes called "trays" or "half cases."

Strong virgin fiber linerboard produced from softwood (typically southern pine) using the kraft pulping process. Kraft linerboard is brown in its natural state and is the strongest grade of linerboard, offering superior compression strength and moisture resistance compared to recycled grades. "Kraft" comes from the German word for "strength."

The flat paperboard facing sheets that are glued to one or both sides of the corrugated medium. The outer liner is the side typically printed or facing outward, while the inner liner faces the product. Liner material is usually linerboard (kraft or recycled) but can also be pre-printed or coated for specific applications.

Paperboard used as the flat facing material in corrugated board construction. Linerboard is manufactured in two main grades: unbleached kraft (brown, from virgin softwood fiber) and recycled (sometimes called test liner, made from recovered fiber). Linerboard basis weights typically range from 26 lb to 90 lb per MSF. It accounts for roughly two-thirds of the fiber in a corrugated box.

A general term for very fine flute profiles, typically E-flute (1.6 mm), F-flute (0.8 mm), G-flute (0.5 mm), and N-flute (0.4 mm). Microflute corrugated board offers thinner, lighter packaging with superior printability compared to conventional B- and C-flute, and competes directly with solid folding carton board for retail and consumer packaging.

A hydraulic burst test that measures the force required to puncture the face of corrugated board, named after the Mullen tester instrument. The result is expressed in pounds per square inch (psi). The Mullen test was the traditional specification method for corrugated boxes (e.g., "200# test") before ECT became the preferred method for most applications. It remains specified for some government and ISTA packaging standards.

Used corrugated boxes and sheets collected for recycling. OCC is the largest single grade of recovered paper by volume and the primary raw material for recycled-content linerboard and medium. OCC prices fluctuate based on domestic demand, export demand (particularly to Asia), collection rates, and contamination levels. The OCC market significantly influences containerboard pricing.

A test measuring the strength of the glue bond between the liner and the fluted medium in corrugated board. Poor pin adhesion indicates insufficient glue application, incorrect glue formulation, or improper temperature/pressure on the corrugator, and can lead to delamination under stress. Measured in pounds of force required to separate the components.

A single layer of linerboard or corrugated medium in the construction of corrugated board. Single wall (single face + one liner) is a 3-ply structure, double wall is 5-ply, and triple wall is 7-ply. Higher ply counts provide greater strength at the cost of increased weight and material.

The most common box style in the corrugated industry, accounting for roughly 80% of all boxes produced. An RSC has four side panels scored and folded from a single sheet, with flaps on the top and bottom that fold to close. The major flaps (from the length panels) meet at the center. RSC is designated as FEFCO 0201 and is the most economical box design.

A linear impression or crease made in corrugated board to allow clean, controlled folding. Scores are created by pressing a blunt rule into the board and are essential for forming box flaps and panels. Score depth and accuracy directly affect box squareness, appearance, and ease of assembly.

Corrugated board with only one liner sheet glued to the fluted medium, leaving the flutes exposed on one side. Single face is used primarily for cushioning wraps, interior packaging, and protective padding. It is the intermediate product created during the first stage of the corrugation process before the second liner is applied.

The standard corrugated board structure consisting of one fluted medium layer between two flat liner sheets, creating a 3-ply construction. Single wall accounts for the vast majority of corrugated packaging produced and is available in all flute profiles (A through F). Typical ECT ratings for single wall range from 23 to 71 ECT.

The ability of a corrugated box to support the weight of other boxes stacked on top of it during storage and transportation. Stacking strength is determined by the box compression test (BCT) and is affected by board grade, flute selection, box dimensions, pallet pattern, humidity, and storage duration. Stacking strength degrades significantly in high-humidity environments.

The Technical Association of the Pulp and Paper Industry, an international professional organization that publishes standardized test methods used throughout the paper and corrugated industries. TAPPI test methods (e.g., T 811 for ECT, T 810 for Mullen burst) are the recognized standards for measuring corrugated board and containerboard properties.

Corrugated board with three layers of fluted medium and four liner sheets, creating a 7-ply structure. Triple wall is extremely strong and rigid, used for heavy-duty industrial shipping (automotive parts, machinery), military specifications, and as a replacement for wooden crates. Triple wall can support loads of 500 lb or more per box.

Wood pulp fiber that has not been previously used in paper or packaging production, as distinguished from recycled or recovered fiber. Virgin kraft fiber (typically from southern pine) produces the strongest linerboard and medium grades. Corrugated packaging may contain any proportion of virgin and recycled fiber depending on strength requirements and cost targets.

An undesirable curvature or bowing in corrugated board caused by uneven moisture content between the liners, or by differences in tension during the corrugation process. Warp creates problems in automatic case erecting, printing registration, and box appearance. The two main types are S-warp (cross-machine direction) and twist warp.

A surface defect in corrugated board where the outline of the flute tips is visible through the outer liner, creating a rippled or wavy appearance. Washboarding is caused by the flute tips pressing against the liner during gluing and is most noticeable in printed areas. It is minimized by using heavier liner weights, finer flute profiles, or pre-print methods.

A box style formed by wrapping a single corrugated blank around the product, then folding and gluing or stapling it closed. Wrap-arounds conform tightly to the product, minimizing void space and material usage. They are commonly used for beverage multipacks, produce trays, and bundled goods.