In our August 5th article "Moisture Permeability = Vapor Permeability = Breathability?", we explained that actually moisture permeability = vapor permeability ≠ breathability. However, currently on the market, waterproof and moisture-permeable products have moisture permeability values ranging from 2000 to 8000. So, does a higher number mean better moisture permeability performance?
The moisture permeability performance of fabrics is mostly represented by the moisture permeability rate, but the test results can vary depending on the testing method and conditions. When different brands use varying test methods to indicate their product’s moisture permeability rate, it leads to inconsistent values and makes it impossible to directly compare the moisture permeability performance across products.
Currently, the national standards for testing moisture permeability performance are:
GB/T 12704.1-2009 Textiles — Test method for water vapor permeability of fabrics — Part 1: Method of desiccant (cup method);
GB/T 12704.2-2009 Textiles — Test method for water vapor permeability of fabrics — Part 2: Method of water method.
Among these, the desiccant method is commonly known as the drying agent method (calcium chloride method), while the water method includes Method A (upright cup method) and Method B (inverted cup method).
Desiccant Method:The mouth of the moisture permeability cup faces upward, with a desiccant placed inside. Under constant temperature and humidity conditions, i.e., temperature (38±2)°C,relative humidity (90±2)%, the weight change of the desiccant is measured.
