ISO 3689:2024

Overview

ISO 3689:2024 - "Paper and board - Determination of bursting strength after immersion in water" defines a laboratory method to measure the wet strength of paper and board by determining their bursting strength after immersion in water. Applicable to most papers and boards, the method requires agreement on immersion time between interested parties and notes that repeating the test after time can give different results. The standard updates previous editions and aligns testing practice with ISO 2758/ISO 2759 burst test equipment.

Key topics and technical requirements

• Scope & principle: Measure bursting strength of a single sheet after immersion to quantify wet strength and the bursting strength retention after immersion (expressed as a percentage versus dry strength).
• Apparatus: Use a burst tester configured per ISO 2758 (papers) or ISO 2759 (boards); specified ranges for expected test pressures are given in the standard.
• Water and conditioning: Use reagent water meeting ISO 14487 and laboratory conditioning according to ISO 187 (23 °C ±1 °C or 27 °C ±1 °C in tropical conditions). For wet testing, pre-conditioning of test pieces is not required.
• Sampling & test pieces: Sample selection follows ISO 186. Prepare test pieces as in ISO 2758/2759. Ten test pieces are standard for the wet test (5 with felt/outer side up, 5 with wire/inner side up).
• Immersion procedure:
  • Immerse test pieces vertically, at least 20 mm below water surface, using a support system to prevent folding or contact with tank sides/each other.
  • Typical immersion times: 1 h, 2 h, or 24 h (with specified tolerances). Immersion time shall be agreed and recorded.
• Excess water removal: After immersion, blot between specified blotting paper and roll once forward and backward with a defined metal roller - then test immediately.
• Results & reporting: Results can be reported as mean wet bursting strength, burst index, or percentage retention. Test report must state immersion time, water temperature, and other test conditions.
• Precision & annexes: The standard includes precision data and an informative annex with support system examples.

Applications and users

ISO 3689:2024 is used for:

• Quality control and acceptance testing in pulp, paper and packaging production
• R&D and material selection where wet performance matters (e.g., packaging exposed to moisture)
• Converters, corrugated board manufacturers, test laboratories, and procurement teams specifying wet-strength requirements
• Compliance checks comparing wet vs dry burst strength for product claims

Related standards

• ISO 2758 - Paper: determination of bursting strength
• ISO 2759 - Board: determination of bursting strength
• ISO 186 - Sampling to determine average quality
• ISO 187 - Standard atmosphere for conditioning and testing
• ISO 536 - Grammage determination
• ISO 14487 - Standard water for physical testing

Keywords: ISO 3689:2024, wet strength testing, bursting strength after immersion, paper and board testing, burst tester, immersion times, wet bursting strength retention.