Is it cooler to wear white clothes in summer? The result may be different from what you think

In the hot summer, we need to consider clothing matching while preventing heatstroke and cooling down. Many people have heard that wearing light-colored clothes in summer is cooler than wearing dark-colored clothes. For example, wearing white clothes is cooler than wearing black clothes because white does not absorb heat, while black does. Is this really the case? What color and material of clothes will keep you cooler?

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Part 1

What color to wear depends on where you are

First of all, we need to know that the metabolism in the human body generates heat, and the human body needs to dissipate excess heat to the surrounding environment in order to maintain homeostasis. There are usually four different heat dissipation pathways to regulate the body's temperature: radiation, conduction, convection, and evaporation. The combined effect of these four methods allows us to have a stable body temperature. However, the role they play varies in different situations. For example, when people are quietly indoors, radiation in the mid-infrared wavelength range is the main way for the human body to dissipate heat; during intense exercise, the body will dissipate most of the heat through the evaporation of sweat.

Schematic diagram of the human body's heat dissipation pathways. Image source: Reference [1]

At the same time, in the process of heat transfer, due to the existence of temperature difference, heat energy will be transferred from high temperature to low temperature. That is to say, when our body temperature is lower than the temperature of the surrounding environment, the human body will absorb heat from the surrounding, and when the surrounding temperature is lower than the body temperature, the human body will radiate heat outward. So what kind of clothes to wear in summer is cooler, not only related to the color of the clothes, but also to the environment where the wearer is.

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If you are outdoors in the blazing sun, the ambient temperature is higher than the human body, and the heat will be transferred from the air to the human body. Wearing light-colored clothes will reduce the degree of heat radiation, so it is cooler to wear light-colored clothes in this situation. Although light-colored clothes can reflect some ultraviolet rays, they are not good at absorbing ultraviolet rays, so wearing light-colored clothes is not suitable for long-term exposure outdoors, because it is easy to get sunburned. In contrast, red clothes can absorb a large amount of ultraviolet rays in sunlight, so when you are outdoors for a long time, wearing red clothes is not only cooler, but also sun-proof.

If you are in an air-conditioned room or on a cloudy day or night in summer, when there is less sunlight and the ambient temperature is lower than the human body temperature, choose to wear dark clothes, which absorb heat quickly and dissipate heat quickly. The absorbed heat will form hot and cold air convection on the body surface, taking away the sweat on the body surface. The evaporation of sweat will absorb heat and quickly remove the heat from the skin surface, making people feel cooler.

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Part 2

The less you wear, the cooler you are?

Many people think that the less you wear in summer, the cooler you will be. But beautiful ladies who like to wear tank tops and shorts, as well as shirtless muscular men, please note that you may not be cooler than those who wear T-shirts.

As mentioned above, the skin can only dissipate heat when the body temperature exceeds the external environment temperature. When the external temperature reaches or exceeds the human body surface temperature, the skin cannot actively dissipate heat because the temperature difference between the body temperature and the air temperature is small or even negative. On the contrary, the skin will absorb heat from the outside, causing the body temperature to rise, making it more susceptible to heat stroke. Therefore, wearing less does not necessarily mean you will be cooler.

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Part 3

The material is also important

In the midsummer, the heat is unbearable, and the human body regulates its body temperature through the evaporation of sweat. In order to facilitate the evaporation of sweat, you should wear clothes with good moisture absorption and breathability in summer. When textiles of different materials are placed in the same environmental conditions, their ability to absorb water molecules from the surrounding environment, that is, their moisture absorption capacity, is different. This is due to the different chemical compositions and molecular structures of different textile fibers. For example, silk fibers have more hydrophilic groups - CONH, while polyester and polypropylene fibers lack hydrophilic groups. The more hydrophilic groups there are, the stronger the moisture absorption capacity of the fiber. According to measurements, when the temperature is 24°C and the relative humidity is around 60%, the moisture absorption capacity of linen fabrics is about 10%, silk fabrics are about 9.5%, cotton fabrics are about 8.5%, vinylon is 3%, and polyester is less than 1%.

Therefore, it is best to choose natural fiber products such as linen, silk and cotton for summer clothing. The higher the density of textiles, the worse the air permeability. For cloth made of the same raw materials, if the density is doubled, the air permeability will be half as good. Therefore, the thinner the summer clothing is, the lower the density is, the better the heat dissipation performance is, and the cooler it is to wear.

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At the same time, considering the convection heat dissipation, wearing loose clothes will be cooler, and the openings such as collars, cuffs, and trouser legs should not be too thin or too tight to facilitate ventilation and heat dissipation. Therefore, tights are not suitable for wearing in summer. Women's dresses and A-line umbrella skirts can be worn boldly, which can absorb and blow air when walking, which is both graceful and cool.

Think about why people in the Middle East choose loose robes as their main clothing? It is because they live in a tropical desert climate with extremely strong solar radiation. If the skin is exposed to the sun, it will be burned quickly. Therefore, it is necessary to cover the whole body. At the same time, the wind outside blows into the loose robe and can quickly spread up and down, creating a chimney effect, promoting air flow, sweeping away the moisture emitted by the body, making people feel cooler and more comfortable.

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At present, with the development of textile technology, a large number of new textile materials have emerged. Scientific researchers use various routes, such as material innovation, fiber engineering, advanced integration technology, new structural design and clothing shape development, to design textile products that can provide better thermal comfort for the human body.

Schematic diagram of thermal regulating textiles Image source Reference [1]

In addition, the integration of advanced textiles with thermal regulation properties with flexible electronic devices and energy harvesting devices is also under development, which also enables the next generation of smart textiles to achieve multiple functions including thermal comfort, sensing, computing, and electronic control. I believe that with the development of technology, there will be various colors and styles of heat-resistant and cooling clothes for us to choose from in the future, and working in high-temperature environments will be more comfortable and safe. I hope that the summer will come soon, where we can enjoy ourselves in the hot sun without having to hide in an air-conditioned room.

References:

[1] Peng Y, Cui Y. (2020).Advanced Textiles for Personal Thermal Management and Energy. Joule.4(4),724-742.

[2] Charkoudian, N. (2016). Human thermoregulation from the autonomic perspective. Auton. Neurosci. Basic Clin. 196,1–2.

[3] Nakamura, K. (2011). Central circuitries for body temperature regulation and fever. Am. J. Physiol. Regul. Integr. Comp. Physiol. 301, R1207–R1228.

[4] Shibasaki, M., Wilson, TE, and Crandall,CG (2006). Neural control and mechanisms of eccrine sweating during heat stress and exercise. J. Appl. Physiol.100, 1692–1701.

Produced by: Science Popularization China

Produced by: Xue Yang (Dalian Institute of Chemical Physics, Chinese Academy of Sciences)

Producer: Computer Network Information Center, Chinese Academy of Sciences

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