What are the standards for cool-feeling textiles? What are the contact coolness factor requirements?

Functional clothing is increasingly popular. Cool textile technology has matured. So, the cool textile function is now practical. The relevant departments made two product standards. They aim to regulate the market and assess cool textiles. One is FZ/T 73067-2020 “contact cool knitted garments”. The other is FZ/T 62042-2020 “cool fabric bedding”. Both standards started on 1 April 2021.

The concept of cool textiles

Cool textiles first appeared in Japan. Then, someone introduced them to the United States. Some American companies develop practical cool fibers from fiber structure and raw materials. They work in fiber research and development. The most well-known is coolmax. It uses “cool” to show the fiber’s cool performance. But coolmax only uses its ability to absorb moisture and dry quickly. It makes the human body’s sweat go away quickly and take some heat with it. This makes people feel dry, rather than cool.

China’s first textile coolness standard is GB/T 35263-2017. The process is called “testing and evaluating textile contact instant coolness performance.” It defines textile coolness as: the textile cools the skin below its temperature. This causes rapid heat loss from the skin. The skin temperature then drops. Nerve endings sense this and tell the brain, creating a cool feeling.

Skin contact textiles can cause rapid heat loss. So, they need good thermal conductivity. But, they must not absorb and warm quickly. Instead, they need to absorb heat slowly and release it quickly. Now, the main methods to make textiles cool-sensitive are to use cool-sensitive fiber. Or, to do cool-sensitive finishing.

Cool Feeling Test

The standard is GB/T 35263-2017. The name of the testing and evaluation is “Cool Feeling Performance.” It is about textiles touching the skin.” It explains how to test and evaluate this performance. This method applies to all fabrics and their products. The test’s principle is that, in the right conditions, a hot test plate touches the specimen. The plate is hotter than the specimen. We measure how the plate’s temperature changes over time. From this, we calculate the contact coolness coefficient (q max). This lets us characterize the specimen’s current coolness. In the warm and cold sensation test, the heating plate is Δt hotter than the test specimen. Like fabrics on skin, place it on the specimen’s surface. The peak heat transfer is q max. A larger value means the skin feels more cool. A smaller value means the skin feels less cool.

Test samples:

We will intercept a sample of 5 pieces. Each will be about 200mmX200mm. They will sit at the ambient temperature of 20 ± 2 ℃ and relative humidity of 65 ± 4%. They will sit there for 24 hours before testing.

Test environment:

The lab has a constant temperature and humidity. The temperature is 20 ± 2 ℃ and the humidity is 65 ± 4%. Wait for at least 1 hour to see if the conditions are right before testing.

Test equipment:

Contact warm and cold sense analyser

 Designed to mimic the sense of touch when the human body touches an object

The heat detection plate touches the specimen with a certain pressure. It mimics the human touch. When a person touches the object, they quantify the weight and contact area of the plate. It is possible to measure the heat transfer process that is as close as possible to the human body’s sense of touch.

Touch screen display of measurement data

The cold and warm sense analyser can do one test automatically. It does 10 tests in a row. This improves accuracy.

 PC connection for data output

Special software displays the q max value. It saves the data in CSV format for each measurement. It can be directly exported to PC for convenient data storage and use.

Test steps:

1. Set the carrier table’s temperature to (20±0.5)℃. Lay the specimen flat on the table with the fabric side touching up.

2. Set the temperature of the heat detection plate at (35±0.5)℃. The temperature (ΔT) of the sample carrier table is 15℃. If you use other temperatures, note them in the report.

3. After the plate reaches the set temperature and stays stable, cut off its heat source. Then, quickly place it upright on the specimen so that the copper plate touches the fabric.

4. record the measured q max and retain the result to 3 decimal places in J/(cm²-s).

Test results:

At ΔT=15℃, the contact coolness coefficient is q max≥0.15. Then, the sample has good contact coolness.

FZ/T 73067 is called “Contact Cool Feeling Knitted Garments”. It divides the cool feeling into three grades. Superior garments have a contact cool feeling coefficient of at least 0.25. First-grade garments have a coefficient of at least 0.20. Qualified garments have a coefficient of at least 0.18. All of these are higher than the requirement of not less than 0.15 in GB/T 35263-2017.