Overview
ISO 9932:2021 specifies laboratory test methods for determining the water vapour transmission rate (WVTR) of sheet materials such as paper and board using two instrumental techniques: the dynamic sweep gas method (Method A) and the static gas (electrolytic) method (Method B). Depending on equipment, the standard covers materials up to 38 mm thickness and WVTRs from 0.05 to 65 g/(m2·d). Annexes provide guidance on saturated saline solutions (Annex A) and calibration (Annex B). ISO 9932:2021 is a minor revision of the 1990 edition and complements gravimetric dish methods (see ISO 2528).
Key topics and technical requirements
- Scope and applicability: Instrumental methods for sheet materials, suitable for very low transmission rates and thicker specimens compared to gravimetric methods.
- Method A - Dynamic sweep gas:
- Principle: One side held at high relative humidity, the other swept by a dry inert gas; moisture in the sweep gas is detected by a sensor (electrical resistance, electrolytic cell or infrared).
- Requirements: sealed test cell, controlled temperature (normally 23 °C ±1 °C or 38 °C ±1 °C), desiccated sweep gas (air or nitrogen), sensitive sensor (detect ~0.05 % RH or better), and calibration specimen.
- Method B - Static gas (electrolytic):
- Principle: Test piece seals a cell containing an electrolytic element; water vapour entering the cell is electrolysed and measured as current (microammeter) per Faraday’s law.
- Requirements: humidity cabinet, stainless steel test cells, electrolytic element construction, control box with microammeter calibrated to g/(m2·d).
- Sampling and specimen preparation: Follow ISO 186 for sampling; prepare multiple test pieces (ten), account for face orientation, edge sealing for composites or thick specimens (aluminium foil tape guidance).
- Calibration and precision: Annex B covers instrument standardization; the document includes a general statement of precision and comparison notes with gravimetric (ISO 2528).
Practical applications and users
ISO 9932:2021 is used where accurate WVTR data are critical:
- Packaging engineers assessing barrier performance of paper, board and laminates.
- Quality control and testing laboratories needing faster results and higher sensitivity than gravimetric dish methods.
- R&D teams developing barrier coatings, composite sheets and multilayer materials.
- Building-materials testing where moisture transmission through panels and sheets affects performance.
- Instrument manufacturers and calibration labs for validating and standardizing WVTR test cells.
Related standards
- ISO 2528 - Gravimetric (dish) method for WVTR.
- ISO 186 - Sampling to determine average quality of paper and board.
Keywords: ISO 9932:2021, water vapour transmission rate, WVTR, dynamic sweep gas method, static gas method, paper and board, test methods, packaging, barrier materials.
Open preview (PDF)Paper and board — Determination of water vapour transmission rate of sheet materials — Dynamic sweep and static gas methods
