ISO 5628:2019 specifies laboratory methods used to determine the bending stiffness of paper, paperboard, and thicker structures such as corrugated fibreboard. It is commonly used to quantify “stiffness under flexure” for packaging, converting, and product-performance requirements where runnability and stackability depend on controlled stiffness.
If you are not sure which loading method (2-point, 3-point, or 4-point) fits your material thickness and product type, contact our team for guidance on a practical test setup and documentation package.
ISO 5628:2019 — Paper and board — Determination of bending stiffness — General principles for two-point, three-point and four-point methods
ISO 5628:2019 is an International Standard that defines three related bending test methods for paper-based materials. The methods differ by the loading configuration, which allows the standard to cover thin paper and paperboard as well as thicker board structures where a different loading approach is preferred.
Because bending stiffness is sensitive to specimen orientation (machine direction vs. cross direction) and to the chosen loading mode, the best results come from matching the method and fixture geometry to the material category and the end-use requirement.
Quick Definition
ISO 5628:2019 is a bending-stiffness test standard for paper and board that includes 2-point, 3-point, and 4-point bending methods, selected based on material type and thickness.
What This Standard Covers
This standard covers determination of bending stiffness for paper and paperboard using defined laboratory bending configurations.
Included methods: Two-point bending, three-point bending, and four-point bending.
Material guidance in the standard: Two-point and three-point methods are intended for lower-thickness paper and paperboard, while a four-point method is recommended for corrugated fibreboard and thicker board structures.
What it does not replace: ISO 5628 provides the bending-stiffness framework and method options; it does not replace product specifications that set pass/fail limits for a specific packaging grade or converting process.
Why This Standard Matters in Testing
Bending stiffness is often a critical functional property for paper-based products because it affects how sheets, blanks, and formed parts behave in handling and in automated equipment. In packaging workflows, stiffness targets can be tied to feeding consistency, crease and fold performance, and the ability of a structure to resist sagging or deformation during use.
Using a recognized standard method also improves comparability between suppliers, production sites, and QC laboratories, especially when customers specify a particular loading configuration and reporting format.
Common Materials, Product Types, or Applications Covered
ISO 5628:2019 is commonly applied where paper and board stiffness needs to be tracked as a quality attribute or a design input.
- Printing and writing papers where stiffness influences handling or downstream converting
- Paperboard and cartonboard used for cartons, sleeves, and folded structures
- Solid boards and thicker boards where stiffness is a performance requirement
- Corrugated fibreboard where higher thickness and structure often point to the four-point method
Common Test or Verification Workflow
Most ISO 5628 testing programs are run as part of incoming inspection, production QC, or product-development verification.
Typical workflow: Select the ISO 5628 loading method based on the material category and thickness range, condition specimens per the cited lab environment practices, test in both machine direction (MD) and cross direction (CD) as required, and report bending stiffness using the method-specific calculation and the agreed units.
Practical reporting caution: Results from different loading modes are not automatically interchangeable, so purchase specifications and customer requirements should be aligned to the exact ISO 5628 method used.
Equipment Commonly Used for This Standard
ISO 5628 bending stiffness work typically uses a dedicated bending stiffness tester or a universal testing machine (UTM) configured with the appropriate low-force load cell and a fixture designed for the selected loading mode.
Common equipment: Bending stiffness / stiffness-under-flexure tester; universal testing machine with 2-point, 3-point, or 4-point bending fixture; low-capacity force measurement suitable for paper and board; displacement/deflection measurement appropriate to the fixture design.
Selection notes that affect quoting: The main drivers are the chosen method (2-, 3-, or 4-point), the specimen width/thickness range (especially for corrugated), and whether you need MD/CD testing with fast changeover for QC throughput.
If you are selecting a bending stiffness tester or configuring a UTM for paper and board stiffness work, you can request a detailed quote for a configuration matched to your sample geometry and method preference.
How to Read This Designation or Revision
Designation format: “ISO 5628:2019” identifies the ISO standard number (5628) and the publication year (2019).
Status and edition awareness: ISO 5628:2019 is published (Edition 3) and has been reviewed and confirmed as current in 2024. Earlier editions such as ISO 5628:1990 are withdrawn, and ISO 5628:2012 is listed as a previous edition.
Best practice for compliance: When a customer specification cites ISO 5628, confirm the year/edition and the loading method (2-point, 3-point, or 4-point) so your equipment setup and reporting match the requirement.
Related Standards, Methods, or Frameworks
Depending on the customer specification and the instrument type, bending stiffness testing of paper and board may also be referenced alongside other paper/board bending standards.
- ISO 2493-1: Bending resistance determination based on a two-point loading principle (often cited when requirements are written around two-point loading and defined bending conditions).
- DIN 53121: A commonly cited beam-method bending stiffness reference for paper and board, including corrugated board use cases in some specifications.
Talk with a test equipment specialist
If you need help matching ISO 5628 to a specific paper grade, board thickness, or corrugated structure—and translating that into a practical fixture and force-range configuration—talk with our team about your application.