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Understanding CAN CGSB 4.157-2014: Standard Test Method for Resistance of Materials to Water Vapour Diffusion
A comprehensive guide to the Canadian standard for measuring water vapour transmission rate in textile materials, including testing protocols, technical requirements, and compliance criteria.
Scope and Purpose
CAN CGSB 4.157-2014, titled Textile Test Methods – Resistance of Materials to Water Vapour Diffusion, is a Canadian standard developed by the Canadian General Standards Board (CGSB) that specifies a procedure for determining the resistance of textile materials to the diffusion of water vapour. This test method, often referred to as the “cup method” (desiccant or water method), measures the steady-state rate of water vapour transmission through a fabric under controlled temperature and humidity conditions. The standard is applicable to woven, knitted, and nonwoven fabrics, as well as coated or laminated textile materials. The primary purpose is to evaluate the breathability of textiles used in garments, protective clothing, and technical textiles, where water vapour permeability is a critical comfort and performance factor.
Key application: CAN CGSB 4.157-2014 is widely used in the apparel industry to assess moisture management, particularly for outerwear, sportswear, and workwear where maintaining a comfortable microclimate near the skin is essential.
Technical Requirements
Test Apparatus
The standard requires a sealed test dish (cup), which holds either a desiccant (for the desiccant method) or distilled water (for the water method). The dish is placed in a controlled atmosphere chamber with specified air circulation. Key apparatus includes:
- Test dish with a known open area (typically 0.00246 m²) and a flange to seal the specimen.
- Analytical balance with a precision of 0.001 g.
- Environmental chamber capable of maintaining 23 ± 1 °C and 50 ± 2 % relative humidity with an air velocity of 0.5–1.0 m/s across the specimen surface.
- Desiccant: anhydrous calcium chloride (CaCl₂) for the desiccant method; distilled or deionized water for the water method.
Test Conditions and Sample Preparation
Table 1 summarizes the required conditions and sample parameters.
| Parameter | Requirement |
|---|---|
| Standard atmosphere | 23 ± 1 °C, 50 ± 2 % RH |
| Air velocity | 0.5–1.0 m/s directed upwards past the specimen |
| Test duration | Minimum of 4 hours after steady state; weightings taken at intervals of at least 1 hour |
| Number of specimens | At least 3 per sample; 5 recommended for statistical reliability |
| Sample conditioning | 24 hours under the test atmosphere before testing |
| Sealing medium | Molten wax or silicone sealant to prevent vapour bypass |
Test Method
The test fabric is sealed over the mouth of a dish containing either desiccant (Method A) or distilled water (Method B). The assembly is weighed periodically to determine the rate of water vapour transfer through the specimen. The result is expressed as water vapour transmission rate (WVTR) in g/(m²·24h) or as water vapour resistance (Rmv) in m²·Pa/W. The standard provides equations for both expressions depending on the method used.
Important: Proper sealing of the specimen is critical. Any leak at the edge will cause erroneously high WVTR values. Always verify the seal integrity visually and by periodic weight checks.
Implementation Highlights
Procedure Steps
- Condition specimens in the standard atmosphere for at least 24 hours.
- Assemble the test dish with the appropriate medium (desiccant or water). Record initial weight.
- Place the specimen on the dish rim, seal with melted wax/ring, and weigh immediately.
- Place the assembly in the chamber for the desired test duration, weighing at hourly intervals after an initial stabilizing period (typically 1 hour).
- Plot mass change versus time; the slope of the linear portion gives the steady-state transmission rate.
- Calculate WVTR or water vapour resistance per the formulas in the standard.
Calculation Example
For the desiccant method, WVTR = (Δm × 24) / (A × t), where Δm is the steady-state mass change in grams, A is the exposed specimen area in square meters, and t is the time interval in hours.
Tip for precision: Use at least 5 weight points in the steady-state region and perform a linear regression. A correlation coefficient (R²) above 0.99 indicates a properly established steady state.
Compliance Notes
Reporting Requirements
Reports according to CAN CGSB 4.157-2014 must include:
- Test method used (desiccant or water).
- Test atmosphere conditions (temperature, RH, air velocity).
- Mean WVTR and/or water vapour resistance with standard deviation.
- Number of specimens tested and any rejected due to leaks or defects.
- Statement of compliance to the standard.
Equivalence with International Standards
CAN CGSB 4.157-2014 is technically equivalent to ISO 15496:2004 (MBS-Method) and shares similarities with ASTM E96/E96M but with specific differences in dish design and air velocity requirements. Laboratories seeking international recognition should note that while the principles align, reporting must clearly reference the specific CGSB standard used. The standard also incorporates modifications for laminated and coated materials, ensuring reliable results across diverse fabric types.
Non-compliance risk: Using an alternative dish size or different desiccant without validating equivalence invalidates the test results. Always adhere to the exact specifications of CAN CGSB 4.157-2014 for certified testing.
Frequently Asked Questions
Q: What is the difference between the desiccant method (Method A) and the water method (Method B) in CAN CGSB 4.157-2014?
A: Method A uses a desiccant to create a vapour pressure deficit, measuring the amount of water vapour diffusing through the fabric into the dish over time. Method B uses distilled water inside the dish to simulate evaporation from the skin. Both yield the same WVTR under ideal conditions, but Method B is more sensitive to variations in air velocity and is often preferred for materials with high water vapour resistance.
A: Method A uses a desiccant to create a vapour pressure deficit, measuring the amount of water vapour diffusing through the fabric into the dish over time. Method B uses distilled water inside the dish to simulate evaporation from the skin. Both yield the same WVTR under ideal conditions, but Method B is more sensitive to variations in air velocity and is often preferred for materials with high water vapour resistance.
Q: Can this standard be used for coated or laminated textiles?
A: Yes. The standard explicitly covers coated and laminated materials. However, the coating side should be placed away from the desiccant (or towards the water) in order to avoid delamination or saturation effects. For asymmetric materials, tests on both sides may be required and reported separately.
A: Yes. The standard explicitly covers coated and laminated materials. However, the coating side should be placed away from the desiccant (or towards the water) in order to avoid delamination or saturation effects. For asymmetric materials, tests on both sides may be required and reported separately.
Q: What is the typical test duration for a standard textile sample?
A: The test usually runs for 4 to 8 hours, but heavy or highly water vapour resistant fabrics may require up to 24 hours to reach a reliable steady state. The standard advises that at least three consecutive weights falling on a straight line confirm steady-state conditions.
A: The test usually runs for 4 to 8 hours, but heavy or highly water vapour resistant fabrics may require up to 24 hours to reach a reliable steady state. The standard advises that at least three consecutive weights falling on a straight line confirm steady-state conditions.
For comprehensive application of CAN CGSB 4.157-2014, laboratories and manufacturers should refer to the full text published by the Canadian General Standards Board and consult with certification bodies for industry-specific requirements.