What exactly is “Ice Silk”? Why does it make us feel cool?

The hot summer is here, and coolness and comfort are one of the main needs of consumers when choosing clothing. In recent years, many businesses have been promoting the concept of "ice silk" in summer, claiming that it can make the wearer feel cooler. So, what is the principle of this material and how does it make us cooler?

01

Ice silk is indeed cool, but only for a while

In fact, there are no relevant national standards or textile industry standards to clearly define the concept of "ice silk". "Ice silk" is just a product name used for marketing. According to the survey of "ice silk" clothing on the market, it can be found that most of these fabrics are woven from chemical fibers such as viscose fiber (also known as rayon or artificial cotton), polyester (also known as polyester fiber), and nylon (also known as nylon).

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Here, we must bring up a professional term for textiles - instant coolness upon contact. The national standard GB/T 35263-2017 "Testing and Evaluation of Instant Coolness of Textiles" defines "instant coolness upon contact" as "the moment when the skin comes into contact with a fabric that is lower than its temperature, causing the skin surface to lose heat quickly and the temperature to drop instantly, and then the cool feeling is reflected to the brain through the temperature-sensitive nerve endings in the skin."

From this we can see that when fabrics below skin temperature come into contact with human skin, the body will feel a momentary cool sensation. This sensation is relatively short, and may only last for a few seconds, tens of seconds or minutes when the fabric is first put on. Once the temperature of the fabric is very close to the temperature of the human body and the two reach thermal equilibrium, the cool sensation disappears.

The principle of cool contact sensation is heat conduction. The human body temperature is higher than the temperature of the fabric. When the two come into contact, heat is transferred from the human body to the surface of the fabric, causing the human body temperature to drop.

Why do some fabrics feel cooler when touched? Generally speaking, there are several reasons:

1) The fiber material with high thermal conductivity will bring a more obvious cool feeling when touching the fabric. The higher the thermal conductivity, the faster the heat conduction when the human body touches the fabric. Among the commonly used ordinary textile fibers, nylon has the highest thermal conductivity, and polyester also has a relatively high thermal conductivity. Adding a small amount of nano-powder of minerals such as jade or mica to the fiber can enhance the cooling function of the fiber by taking advantage of the good thermal conductivity and slow heat absorption of these minerals;

2) The cool feeling brought by the smooth and smooth fabric will be more obvious at the moment of contact. The contact area of ​​the smooth and smooth fabric surface is larger, and the heat dissipation rate is faster;

3) From the perspective of post-finishing technology, the use of cooling finishing agents to treat the fabric surface can also increase the cool feeling at the moment of contact by increasing the heat conduction rate.

However, as mentioned above, although this type of fabric can make people "cool for a while", this cool feeling often passes quickly. Fortunately, there are still many ways to keep us cool for a little longer.

02

Not just cool for a while, but cool for the whole summer

When consumers buy clothing and bedding in the summer, they should not just rely on the cool feeling of the fabric when touching it. They should pay more attention to whether the fabric has a continuous heat dissipation function. There are three main ways to achieve continuous heat dissipation: moisture absorption and perspiration, fast heat conduction and external physical cooling. You can also combine multiple methods.

Let's briefly explain this with an example.

There are many products that use moisture absorption and perspiration to continuously dissipate heat, which can be divided into two categories: natural fibers and chemical fibers.

Let's first talk about hemp fiber among natural fibers. This is a preferred natural material for summer clothing. Flax, hemp, and ramie are all good choices. Taking flax as an example, flax fiber has good moisture absorption and perspiration conduction, and has natural antibacterial and deodorizing functions. The cross section of the fiber is irregular polygonal, and the cellulose cells have a central cavity structure, which is arranged in parallel and bonded together by pectin in the fiber.

The irregular external structure and internal cavity structure of this fiber help to form a capillary effect, speeding up the moisture conduction and perspiration discharge. Sweat evaporates on the fiber surface and absorbs the surrounding heat, making the human body feel cool and comfortable. It is more comfortable to use on clothing or bedding.

Cross section of flax fiber and longitudinal fiber morphology under a microscope

Image source: Yan Huina, Zhao Feng, Xing Mengyang, Wu Ziying. Research on identification of two kinds of hemp fibers in cultural relics[J]. Journal of Zhejiang Sci-Tech University (Natural Science Edition), 2017, 37(02): 185-189.

Longitudinal hollow morphology of flax fibers under a microscope

Image source: Zhao Yutao, Huang Yangdong, Deng Zhongmin. Automatic detection of cotton and flax fibers based on image processing[J]. Cotton Textile Technology, 2019, 47(09): 7-12.

The moisture absorption and perspiration wicking function of chemical fibers is achieved by improving the capillary effect through special-shaped cross-sections. For example, hollow fibers, cross-shaped cross-section fibers, triangular cross-section fibers, etc. are a common way to enhance the moisture conduction and perspiration wicking and body heat diffusion functions of fabrics. Special-shaped cross-section chemical fibers modified by artificial physics will help to form a capillary effect, which will speed up the moisture conduction and perspiration wicking. At the same time, the special-shaped cross-section increases the specific surface area of ​​the fiber, which speeds up the evaporation rate of sweat, making the human body feel dry and cool.

This type of fiber is a series of polyester fiber products with excellent moisture absorption and perspiration wicking functions, and is often used in sports knitwear. For example, some fibers have a cross-shaped cross section and four grooves on the surface, which accelerates the diffusion and evaporation of sweat from the body surface to the fabric surface.

Some mats on the market now are woven with ultra-high molecular weight polyethylene fibers. Because these fibers have fast heat conduction and a smooth surface, they have a continuous cool feeling similar to that of bamboo mats in an environment below body temperature.

Clothing equipped with external cooling devices can also cool the human body. For example, individual combat uniforms equipped with a liquid cooling system or an air cooling system and an external power supply can provide soldiers with long-lasting cooling in hot environments; vests designed with ice pack pockets can hold multiple ice packs to quickly cool the front and back of the human body, and can achieve long-lasting cooling by replacing ice packs.

Textile science is also constantly exploring ways to enhance the moisture-wicking performance of fabrics by adopting new fibers, changing the chemical and physical structure of fibers, innovating fabric composition and weaving structure, and adopting new finishing technologies. In order to be as comfortable as possible, consumers can choose suitable clothing according to the usage scenario when purchasing clothing.

For example, when you are going to do a lot of exercise, you should choose moisture-absorbing and quick-drying knitted fabrics; when you are doing daily activities in the office in the summer (where there is air conditioning and it is cooler), you can choose cotton fabrics; when you are doing a little bit of activities outside, you can choose fabrics made of cotton and linen blends or viscose fibers; if you need to be active in the sun, you also need to consider choosing fabrics with strong sun protection functions to protect your skin from sunburn.

Author: Song Lidan, Consulting Engineer, Industrial Research Department, China Textile Construction Planning Institute

Review | Zhang Jie, Chief Engineer, China Textile Construction Planning Institute

Editor | Ding Zong

This article is produced by the "Science Rumor Refutation Platform" (ID: Science_Facts). Please indicate the source when reprinting.

The pictures in this article are from the copyright gallery and are not authorized for reproduction.

Main references:

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