Paperboard Grades and Properties

A technical overview of paperboard families, physical characteristics, and surface treatments for packaging applications.

Paperboard is the structural foundation of most folding carton packaging. Understanding how different grades are manufactured, how their physical dimensions relate to performance, and how surface treatments affect printability and protection helps buyers and engineers specify the right material for each application.

What Paperboard Is

Paperboard is a thick, stiff sheet material produced from cellulose fiber, distinguished from standard paper primarily by its caliper — its measured thickness — and the multi-ply furnish constructions that give it structural rigidity. Unlike corrugated fiberboard, which achieves its strength through a fluted medium sandwiched between liners, paperboard is a solid sheet. This makes it suitable for folding carton applications where a smooth exterior, tight dimensional tolerances, and a clean fold are required.

The fiber furnish — meaning the source and processing of the pulp — determines many of the board's fundamental properties, including whiteness, surface cleanliness, and the degree to which it can accept coatings or printing inks. Paperboard is produced on large multi-wire or cylinder-mold machines that lay down multiple plies simultaneously, allowing manufacturers to engineer a board with different fiber characteristics on the face, back, and inner plies. This layered construction is what separates it from single-ply paper and gives structural designers the ability to predict bending stiffness, score behavior, and creasing performance. The properties of paperboard as a material are summarized at https://en.wikipedia.org/wiki/Paperboard.

Major Grade Families

Solid bleached sulphate, commonly abbreviated SBS, is manufactured entirely from virgin chemical pulp that has been bleached to a high degree of brightness. The result is a board with a very clean, white appearance throughout its caliper. Because no recycled fiber is incorporated, SBS tends to exhibit consistent surface smoothness and is well suited to applications where direct food contact, high-fidelity graphics, or strict odor and contamination requirements apply.

Coated recycled board, known as CRB, and its relative coated-on-one-side newsback, sometimes called CCNB, are produced from a furnish substantially or entirely composed of recovered fiber. The inner plies carry a gray or mottled appearance due to the mixed fiber sources, while the face is coated to provide a printable surface. These grades are widely used in consumer product packaging where the carton interior is not visible and where sustainability commitments favor recycled content.

Unbleached kraft grades, designated in various markets as SUS or CUK, are produced from virgin kraft pulp that has not been bleached, retaining the natural brown color of the fiber. Unbleached grades generally exhibit high tear and tensile strength relative to their weight, attributable to the long, intact fibers preserved through the kraft cooking process. They are used where strength is prioritized alongside a natural aesthetic.

Caliper and Basis Weight

Caliper is the measured thickness of a paperboard sheet, typically expressed in points or thousandths of an inch in North American practice, or in micrometers in metric contexts. It is one of the primary variables a structural engineer uses to predict carton performance, because bending stiffness increases sharply with thickness. Even modest increases in caliper can therefore produce substantially stiffer cartons, all else being equal. Caliper must be consistent across the width and length of a roll or sheet to ensure predictable performance on converting equipment.

Basis weight measures the mass of a defined area of board and is expressed in different unit systems depending on the market. While basis weight and caliper are related, they are not interchangeable descriptors. Density varies between grade families and even between furnishes within a grade, so two boards with identical basis weights may differ noticeably in caliper and therefore in stiffness. Buyers specifying board for a given carton structure must consider both dimensions together rather than relying on weight alone as a proxy for structural performance. The lamination processes mentioned here are described at https://en.wikipedia.org/wiki/Lamination.

Coatings and Barriers

The printable surface of most commercial paperboard is achieved through the application of clay-based coatings, which fill the microscopic voids in the fiber mat and create a smooth, receptive layer. Coating weight affects both print quality and the overall caliper of the finished sheet. Higher coating weights generally improve ink holdout and color density but also add to cost and weight. Coatings may be applied in a single pass or in multiple layers, with top coats providing a final surface optimized for the specific printing process the carton will undergo.

Beyond surface appearance, many applications require the board to resist transmission of moisture, grease, or other substances that would otherwise migrate through the substrate. These functional barriers are applied as coatings or laminates after the base board is manufactured. Aqueous barriers, wax treatments, and polymer extrusion coatings each offer different performance profiles with respect to temperature resistance, recyclability, and barrier level. The choice of barrier system interacts with other downstream requirements, including whether the carton will pass through a heat-seal station, whether it needs to be repulpable, or whether it will contact food directly.