Overview
ISO 12572:2016 specifies the cup method for measuring water vapour transmission properties of building materials and products under isothermal conditions. The standard defines procedures to determine water vapour permeance, water vapour permeability, water vapour resistance, water vapour resistance factor (μ) and water vapour diffusion‑equivalent air layer thickness. Test results are intended for use in design, production control and inclusion in product specifications and apply to both hygroscopic and non‑hygroscopic materials, including insulation, faced products and materials with integral skins.
Key topics and requirements
- Test principle: Sealing a specimen to an open cup containing either a desiccant (dry cup) or a saturated aqueous solution (wet cup). The assembly is placed in a temperature‑ and humidity‑controlled chamber; periodic weighings determine steady‑state vapour flow.
- Isothermal test conditions: Different sets of temperature and relative humidity conditions are specified for reproducible results.
- Specimen preparation: Requirements for specimen shape, exposed area, thickness, conditioning and the number of specimens to be tested.
- Apparatus and sealing: Corrosion‑resistant test cups (glass or metal), templates and sealants; special cup designs and sealing techniques for different material types are given in annexes.
- Calculations and reporting: Methods to calculate mass change rate, vapour permeance, permeability (for homogeneous materials), resistance, resistance factor and diffusion‑equivalent air layer thickness.
- Accuracy and control: Guidance on specimen area and thickness, weighing precision, environmental control (temperature, humidity), effects of barometric pressure and corrections for air layers and masked specimen edges.
- Annexes: Normative annexes provide tailored methods for self‑supporting materials, loose fills, membranes/foils, mastics/ sealants, coatings, and corrections for edge effects and air layer resistances.
Applications and users
ISO 12572:2016 is used by:
- Materials and product manufacturers for product development, performance declaration and production control.
- Independent testing laboratories conducting standardized water vapour transmission testing (cup method).
- Building designers and hygrothermal modelers requiring reliable vapour permeance/permeability data for building envelope design and moisture control.
- Specifiers and compliance officers who include water vapour properties in product specifications and regulatory documentation.
Practical applications include evaluating insulation performance, selecting appropriate vapour control layers, specifying vapour‑permeable membranes and validating coating and sealant vapour transmission characteristics.
Related standards
- ISO 9346 (terms and definitions related to hygrothermal performance) is cited for terminology used in ISO 12572:2016.
Keywords: ISO 12572:2016, cup method, water vapour permeance, water vapour permeability, hygrothermal performance, water vapour transmission, building materials, vapour resistance factor.
Open preview (PDF)Hygrothermal performance of building materials and products — Determination of water vapour transmission properties — Cup method
