ISO 3781:2011 is a test method for determining the wet tensile strength of paper or board after immersion in water for an agreed period of time.
It is commonly used to compare wet-strength performance for paper and board grades intended to be handled, converted, or used in damp or wet conditions, and it can also be used to calculate wet tensile strength retention versus dry tensile strength. If you need help aligning the correct edition and tensile method option to your workflow, contact our team.
ISO 3781:2011 — Paper and board — Determination of tensile strength after immersion in water
ISO 3781 specifies how to measure the tensile strength of paper or board after soaking in water, producing a wet tensile strength result and (when required) a retention value compared to dry tensile strength.
The soaking time is selected to suit the material and the intended end-use conditions, and it must be defined and reported with the results.
Quick definition
Standard type: Test method.
What it measures: Wet tensile strength (force per unit width) after immersion, and optionally wet tensile strength retention versus dry tensile strength.
Primary purpose: Compare wet-strength performance for paper/board products where exposure to water is expected during converting, handling, or end use.
What this standard covers
ISO 3781 applies to paper and board, with an agreed soaking time that is long enough to reach the intended level of saturation for the grade under evaluation.
It is not intended for tissue and tissue products (and other lightweight, highly absorbent papers that are difficult to handle or have very low wet strength), where other methods are typically used.
Why this standard matters in testing
Wet tensile performance is often a pass/fail or supplier-qualification characteristic for packaging and paper products that may see water contact, humidity, wash-down, condensation, or wet converting steps.
Because wet tensile results can be sensitive to soaking time, water temperature, and clamping/slip behavior during the pull, ISO 3781 helps teams standardize preparation and reporting so results are more comparable across labs and production sites.
Common materials, product types, or applications covered
ISO 3781 is commonly specified for paper and board grades where wet handling strength matters, such as wet-processed or water-exposed packaging components, certain label/laminate structures, and strength-treated paper/board products.
It is also used in R&D and QA/QC to compare the effectiveness of wet-strength chemistries or surface treatments by reporting wet tensile strength retention alongside dry tensile strength.
Common test or verification workflow
Most ISO 3781 workflows follow a controlled sequence that ties wet testing back to a recognized dry tensile method.
Common workflow steps: Sample and condition paper/board as required; prepare tensile strips for machine direction (MD) and cross direction (CD); soak strips in specified water for the agreed time; blot to remove surface water; test immediately using a constant-rate-of-elongation tensile method; calculate wet tensile strength and, if required, wet tensile strength retention versus dry tensile strength.
What to document: Soaking time, water temperature/condition, tensile method used (including test speed option), MD/CD orientation, and any deviations that could influence clamping or saturation behavior.
Equipment commonly used for this standard
ISO 3781 typically points to a constant-rate-of-elongation tensile test setup suitable for paper and board, plus simple wet-prep accessories to control soaking and handling.
Common equipment: Constant-rate-of-elongation tensile tester or universal testing machine configured for paper/board tensile; paper grips designed to minimize slip and edge damage (often pneumatic grips for consistent clamping pressure); appropriately sized low-capacity load cell; specimen cutter or strip die for consistent width; soaking dish or bath and water meeting the referenced water quality; blotting materials; conditioning space or chamber for dry-state preparation when required.
Quoting and configuration caution: The grip style and pressure control are often as important as machine capacity—paper can slip when wet, and board can require higher clamping force. If you are selecting grips and load cell capacity for MD/CD wet tensile work, you can request a detailed quote for a configuration matched to your grade range and reporting needs.
How to read this designation or revision
Designation: ISO 3781:2011.
What the “2011” means: The year indicates the published edition of the standard. ISO 3781:2011 is the current published version and has been reviewed and confirmed as current by ISO (most recently confirmed in 2022).
Revision sensitivity: Wet tensile testing is sensitive to method details (including which companion tensile procedure is used and what soak time is specified). Purchase specifications should cite the exact edition and define the soaking time and reporting expectations.
Related standards, methods, or frameworks
ISO 3781 is commonly used alongside ISO paper and pulp laboratory practices for sampling, conditioning, and tensile testing. In many lab workflows, dry tensile testing is performed using a referenced tensile properties method, and wet tensile strength retention is calculated by comparing wet results to dry results from the same material.
- ISO 1924-2 and ISO 1924-3 (tensile properties, constant-rate-of-elongation methods)
- ISO 186 (sampling of paper and board)
- ISO 187 (standard atmosphere for conditioning and testing)
- ISO 14487 (standard water for physical testing)
- ISO 12625-5 (wet tensile strength for tissue, where applicable)
Talk to our team about ISO 3781 testing setups
If you are building or upgrading a wet tensile testing station for paper or board—especially where grip selection, clamping pressure control, or MD/CD throughput matters—talk with our team about an equipment package aligned with ISO 3781 and your grade range.