How to talk about the advantages and disadvantages of moisture permeability? ——Revealing the secret of moisture permeability numerical labeling

In fact, moisture permeability = vapor permeability ≠ breathability. However, the waterproof and moisture permeable (WeChat: Deco Nano) products currently on the market have moisture permeability values ranging from 2000 to 8000. So, does the higher the value, the better the moisture permeability performance?

The moisture permeability performance index of fabrics is mostly characterized by moisture permeability. The moisture permeability test value varies with different test methods and test conditions. When each merchant uses different testing methods to characterize the moisture permeability of the product, it will lead to moisture permeability. High and low, it is impossible to horizontally compare the moisture permeability performance of the products.

Standard for moisture permeability test method

At present, the national moisture permeability test standard is:

GB/T 12704.1-2009 Textiles – Test method for moisture permeability of fabrics – Part 1: Moisture absorption method;

GB/T 12704.2-2009 Textiles – Test methods for moisture permeability of fabrics – Part 2: Evaporation method.

Among them, the hygroscopic method is commonly known as the desiccant method (calcium chloride method), and the evaporation method also includes method A, the straight cup method, and method B, the inverted cup method.

The main difference between hygroscopic method and evaporation method

Moisture absorption method: With the mouth of the moisture-permeable cup facing upward, place the desiccant inside, and measure the weight change of the desiccant under constant temperature and humidity conditions, that is: temperature (38±2)°C, relative humidity (90±2)%.

Evaporation method: Fill a moisture-permeable cup with distilled water, and measure the change in water weight under constant temperature and humidity conditions, namely: temperature (38±2)°C and relative humidity (50±2)%.

Method A: Positive cup method: When testing, the mouth of the cup is facing upward, there is still air between the water and the fabric, and there is also an air layer on the outer surface of the sample. The diffusion resistance of water vapor in the static air layer is relatively large, so it is obtained by the positive cup method. The moisture permeability is relatively small.

Method B: Inverted cup method: When testing, the mouth of the cup is facing downwards, and the water is in direct contact with the surface of the sample, which eliminates the diffusion resistance of the air layer in the cup to water vapor, promotes the absorption of water by the film or coating, and accelerates moisture permeability, so the test The moisture permeability obtained is greater than that of the straight cup method.

Similarly, experiments have shown that if it is a coated or film-coated product, the weight added by the desiccant is usually less than the weight lost by the water in the cup, so the moisture permeability obtained by the evaporation method is relatively greater than the hygroscopic method.

Thoughts on the applicable scope of the standard

Generally speaking, the order according to the moisture permeability value is: evaporation method > moisture absorption method, inverted cup method > straight cup method.

The test conditions of the evaporation method and the cupping method are similar to the moisture permeability of clothing worn by the human body at rest and with a small amount of movement, when the human body sweats less. The inverted cup method is closer to the moisture permeability of the human body during strenuous exercise, when the human body excretes more sweat.

Source: Outdoor Technology