SBS, CUK and CRB describe paperboard families. They help narrow a material search, but they do not establish a universal ranking for stiffness, cost, food-contact suitability or environmental performance.
Select the supplier grade against the carton drawing, converting process and end use. Compare actual data at the caliper you intend to buy.
1. SBS (Solid Bleached Sulfate)
SBS is made from bleached virgin chemical pulp and has a white appearance through the sheet. Coated versions provide a surface for detailed graphics and finishing. It is used in applications including cosmetics, healthcare and food packaging.
The white base can be useful when the inside is visible or print color consistency matters. It does not establish that a particular board is odor-free or suitable for every food-contact condition. Those are separate requirements.
2. CUK (Coated Unbleached Kraft)
CUK uses unbleached kraft fiber, generally with a brown reverse and a coated printing face. Strength and tear resistance are reasons to evaluate it for beverage carriers and demanding retail packs.
CUK does not automatically mean wet-strength board. Specify any wet exposure, barrier treatment or carrier-handle requirement and obtain evidence for that finished grade. Supplier names such as SUS or CNK may describe related products; confirm the exact construction rather than assuming every acronym is interchangeable.
3. CRB (Coated Recycled Board)
CRB uses recovered fiber, often with a white top layer and coated print surface. It appears in many dry-product and household-goods cartons.
Recycled furnish is not itself proof of poor converting performance. Compare crease quality, stiffness in both directions, surface requirements and variation for the actual grade. Nor does “recycled” identify a precise post-consumer percentage unless the supplier declares it.
The family descriptions above are supported by the Paperboard Packaging Council’s grade reference. Its examples are common uses, not approvals for a specific pack.
4. Other Grades: FBB and Non-Bending Board
Folding boxboard (FBB) is another cartonboard family. Evaluate the specific product’s stiffness, basis weight and surface data; Metsä Board’s FBB product range provides an example of grade-specific supplier documentation.
Non-bending chipboard is often used as body stock for rigid boxes, covered with a separate printed wrap. It should not be substituted directly for a folding-carton grade that must crease and erect on a packing line.
5. Specification Basics: Caliper vs. Basis Weight
These measurements answer different questions:
| Property | Meaning | Example or unit |
|---|---|---|
| Caliper | Thickness under a defined measurement method | 18 pt = 0.018 in = 0.4572 mm |
| Basis weight or grammage | Mass per unit area | g/m², or lb per stated ream area |
| Bending stiffness | Resistance to bending under the stated test | Specify machine and cross directions, method and units |
| Bulk | Thickness relative to grammage | Requires consistent units and test conditions |
| Yield | Usable area per unit mass | Useful when comparing material consumption |
Scroll to compare all columns.
Basis weight is not density. Equal caliper does not guarantee equal stiffness, and equal grammage does not guarantee equal caliper. For a folding carton, grain direction, scores, cutouts and the erected structure also affect performance.
A Material-Yield Example
Assume a blank area of 0.08 m², before production waste:
- At 300 g/m², board mass per blank = 0.08 × 300 = 24 g.
- At 350 g/m², board mass per blank = 0.08 × 350 = 28 g.
- The difference is 4 g per blank, or 400 kg per 100,000 blanks.
These are illustrative numbers. A lighter blank is only a useful alternative if it meets the same converting, protection and appearance requirements. Include waste, coatings and purchasing units when converting the comparison into a quotation.
6. What to Ask the Supplier
- Grade name, mill and allowed substitutions.
- Caliper and grammage tolerances, with test methods.
- Machine- and cross-direction stiffness data at the proposed caliper.
- Recommended grain direction, crease settings and glue compatibility.
- Surface, rub and barrier performance required for the application.
- Recycled-content declarations and the basis for any environmental claim.
- Documentation for the intended direct-food-contact conditions, if applicable.
For U.S. food applications, the FDA explains how to determine the regulatory status of food-contact components. A board-family acronym is not that determination; coatings, inks, adhesives, food type and conditions of use also matter.
7. Qualify the Converted Carton
Trial the selected board on the actual printing, creasing, gluing and packing process. Check fit, squareness, opening force, closure retention and appearance with representative product. Keep the approved sample and specification together so a material substitution triggers a meaningful comparison.
Continue with Carton Builder for a preliminary structure and folding carton role and limits for the loads that still need validation.