It’s so thin that it’s transparent! Can such sun protection clothing still protect against the sun?

Reviewer: Yang Yuqiu

Professor of Textile Materials Department, College of Textiles, Donghua University

In the hot summer, the sun is lavishing its enthusiasm. Sunlight can accelerate the synthesis of vitamin D, promote the development of bone tissue, prevent rickets, benefit health, and tan our skin into a wheat color... Although sunlight has many benefits, it also has harm to the human body.

The UVA band of ultraviolet rays in sunlight has strong penetrating power and can reach the dermis of the skin, causing wrinkles and aging; the frequency of UVB is slightly higher, and excessive exposure may cause rashes and burns; the frequency of UVC is even higher, and it may even affect white blood cells and cause skin cancer.

Source: Baidu Encyclopedia

When it comes to sun protection, many people will choose sunscreen, sun umbrellas, sun protection clothing and other sun protection products. A common view is that physical sun protection is better than chemical sun protection, and sun umbrella + mask + hat + sun protection clothing is called the "hardest sun protection" combination. Sun umbrellas, masks and hats are commonplace, but how does the legendary "sun protection clothing" protect us from the harm of ultraviolet rays?

Source: A shopping website

The difference between sun protection clothing and ordinary clothes

Sun protection clothing usually follows two major sun protection principles. One is to apply a sun protection coating to the outer layer of the clothing to increase the fabric's reflection and scattering of ultraviolet rays; the other is to add ultraviolet absorbers to the fibers to convert the electromagnetic energy contained in ultraviolet rays into heat energy and harmless low-energy radiation. As people's requirements for clothing comfort increase, good sun protection clothing should not only have anti-ultraviolet properties, but also have good comfort properties.

Source: Baidu Image Library

How to judge the quality of sun protection clothing?

Open the shopping app, and you will see a wide variety of sun-protection clothing. How do you judge the quality of sun-protection clothing?

1. According to the provisions of my country's "Evaluation of UV Protection Performance of Textiles": sun protection clothing must meet the following standards at the same time: the product's total ultraviolet protection factor (UPF) is greater than 40 (this index includes the absorption and reflection of UVA and UVB) and the long-wave ultraviolet (UVA) transmittance is less than 5%. When buying sun protection clothing, friends should pay attention to the UPF value on the label. The higher the UPF value, the better the protection effect of ultraviolet rays. (The evaluation index of medium-wave ultraviolet rays (UVB) is more used in sunscreens, such as higher-level protection such as 30+)

Source: A shopping website

2. Breathability: Gas mainly passes through the gaps between fibers and the pores between yarns. The breathability of sun-proof clothing is closely related to the morphological structure of the yarn and the organizational structure of the sun-proof clothing.

Generally speaking, the finer the textile structure of the fabric used in sun-proof clothing, the higher the sun protection effect. However, if the textile structure of sun-proof clothing is too fine, it will lead to poor air permeability and seriously affect the wearing comfort, so the fineness of the textile texture of sun-proof clothing needs to reach an optimal balance value. In general, the air permeability value of sun-proof clothing should be greater than 60 mm/s to ensure wearing comfort.

The honeycomb structure in the picture below utilizes the spatial textile tissue effect to achieve both sun protection and breathability. That is to say, if this piece of fabric is projected onto a plane, no pores can be seen on this plane (they are blocked by fibers, intercepting the straight-line propagating sunlight), but there are pores in three-dimensional space, which allow body moisture and external dry air to be exchanged inside and outside.

Source: A shopping website

3. Washing resistance: There are two main aspects: on the one hand, washing will cause changes in the size of the sun-proof clothing, such as loosening or washing away small fibers, which will increase the porosity between fibers or yarns. Then the amount of ultraviolet rays directly passing through the pores of the sun-proof clothing will increase significantly, thereby reducing the anti-ultraviolet performance of the sun-proof clothing; on the other hand, the sun-proof coating in the sun-proof clothing will be lost with the increase in the number of washings, causing the sun-proof clothing to gradually lose its anti-ultraviolet performance.

4. Contact feeling of cold and warm: When the sunscreen clothing touches the human skin, the two will produce heat exchange due to the different temperatures. If the temperature of the sunscreen clothing surface is lower than the temperature of the skin surface, it will produce a contact feeling of cold, and vice versa, it will produce a contact feeling of warm. In the hot summer, the stronger the contact feeling of cold, the more comfortable the sunscreen clothing is. Only those materials that can quickly transfer heat and absorb the ultraviolet spectrum are conducive to the preparation of comfortable and cool sunscreen clothing.

Source: A shopping website

5. Hygroscopicity: When the external temperature is high, a large amount of water in the human body will evaporate and dissipate heat. If this evaporative heat cannot be absorbed and dissipated in time, people will feel stuffy and uncomfortable. Therefore, the hygroscopicity of sun-proof clothing is an important factor in evaluating its comfort.

This is why people like to wear cotton clothes in summer. Compared with chemical fibers such as polyester that have anti-ultraviolet agents added inside the fibers, cotton fibers have excellent moisture absorption and can absorb sweat into the cavities of cotton fibers to keep the surface dry. However, the anti-ultraviolet performance of cotton fibers themselves is one of the poorest among all types of clothing fiber raw materials.

6. Moisture permeability: The moisture permeability of sun-proof clothing is an important indicator for evaluating the moisture absorption and perspiration of sun-proof clothing. The characterization indicator of the moisture permeability of sun-proof clothing is the moisture permeability rate. The higher the moisture permeability rate of the sun-proof clothing, the better the moisture permeability.

Source: pexels

Although cotton fibers have excellent moisture absorption and breathability, in recent years chemical fibers (mainly polyester) have developed grooves on the surface. These grooves can store a large amount of sweat excreted by the body and quickly discharge it into the external environment under the action of air circulation. This is what people often refer to as "moisture absorbing and quick-drying" when evaluating sports fabrics or clothing.

Finally, a reminder! In the hot summer, the heat is unbearable. Friends, while enjoying the summer, please pay attention to sun protection! Chemical fibers with UV absorbers and fabrics with sunscreen treatment can make comfortable sun protection clothes, but it is still recommended that you carry a sun umbrella with you. Avoiding direct exposure to the sun for more than 20 minutes is also a good way to prevent sunburn.