In the winter warm clothing market, many close-fitting underwear are marked with the function of "sentimental heating", claiming that the clothing itself can heat up and heat the human body. So is this " self-heating " function real?
From the perspective of the law of conservation of energy, heat is of course impossible to produce out of thin air, so there is no "spontaneous heating" clothing that can "create something out of nothing". However, there are indeed many types of heating fiber materials that can provide us with a little extra warmth under some conditions. Clothes with these materials do not need to be particularly thick, and they are particularly warm when worn.
picture gallery copyright pictures, reprinting
without authorization, so how do these magical materials produce heat? What should we pay attention to when we wear and wash these clothes? Let’s reveal the secret today!
01
Magical heating fiber
There is no doubt that all kinds of self-heating fibers are actually heated with the help of external forces. For example, light energy heating fibers rely on absorbing sunlight and reflect the heat radiation of the human body; electrical heating fibers heat when they are energized; phase change fibers use the phase change of substances to release or absorb latent heat to adjust the temperature. However, the most commonly used heating mechanism in daily clothing is "hygroscopic and heat". Hygroscopic heating fibers mainly absorb water vapor, that is, sweat, and form hydrogen bonds and to emit heat. In the structure of fibers, there are some hydrophilic —which can be simply understood as “water-like” —that will combine with water molecules to generate heat, and the kinetic energy of water molecules will also be converted into heat.
hydrogen bond is a special chemical bond between the intermolecular force and the covalent bond of . Usually it is more common in water. The hydrogen bonds in the solid water (ice, left of the picture above) are more stable, while the hydrogen bonds in the liquid water (right of the picture above) will be constantly broken and recombined. Common textile fibers have the ability to absorb hygroscopic heat, but the heating abilities of different varieties vary. Specialized self-heating fibers have more hydrophilic group in the chemical composition, and the fibers have better hygroscopic properties and more heat emitted after hygroscopic absorption. In order to improve the hygroscopic properties of the fiber, not only can the fiber be added to the hydrophilic group for hydrophilic treatment, but also can change the surface morphology and structure of the fiber to facilitate the adsorption of water molecules on the surface of the fiber. For example, by increasing the number of grooves and depth of the fiber surface, the adsorption capacity of the fiber to water vapor is improved. In the figure below, the two hygroscopic heating fibers on the right side have the number and depth of surface grooves that exceed the ordinary acrylic fiber on the left.
The morphology of different fibers under scanning electron microscope . Image source: References [1]
Hygroscopic heating fibers exothermic through moisture absorption, but after the fiber "sucks" moisture, its exothermic reaction will slow down. The hygroscopic fibers will also discharge moisture, and this process will absorb heat. If the moisture cannot be dehumidified in time, the moisture-absorbing fibers will cause discomfort to the wearer. Therefore, in order to improve this discomfort, many fabrics use moisture absorption and heating fibers and other types of fibers to achieve a balance between moisture absorption, heat removal and dryness. For example, acrylic fibers and polyester fibers and .
There are many types of self-heating underwear, screenshot from a certain e-commerce website. So, in the face of a wide range of self-heating underwear products, how should we choose?
02
Self-heating clothing has "standard"
Although, there is currently no mandatory standard for hygroscopic heating underwear in my country, you can refer to the industry standard FZ/T 73036-2010 " hygroscopic heating knitted underwear " to evaluate hygroscopic heating underwear. This standard proposes two indicators on hygroscopic heating performance. One is that the maximum temperature rise value is greater than or equal to 4.0℃, and the other is that the average temperature rise value is greater than or equal to 3.0℃ within 30 minutes. When purchasing hygroscopic heating underwear, consumers should pay attention to preventing exaggerated publicity from merchants and choose formal channels and trustworthy brands. In addition, underwear that meets the standards will be clearly marked in the standard column on the product tag, and it will comply with the FZ/T73036-2010 "Hydrink Knitted Underwear" standard, which can be used for reference when purchasing.For infants and young children with delicate skin, it is not recommended to wear moisture-absorbing and heating underwear, because moisture-absorbing and heating underwear reciprocates in the hygroscopic-heat-exhaust-heat cycle, which can easily cause skin discomfort in infants and young children.
Standard description of certain hygroscopic heating clothing. In addition, clothing containing electrical heating fibers is also a good choice. Generally, there are metal fibers, carbon fibers, , and composite heating fibers. The principle is similar to that of an electric blanket: it is woven into the fabric, or made into a special heating unit and sewed into the clothes mezzanine. It can continuously supply power through an external power supply, and the electric energy can be converted into heat and transferred to the human body. Electric heating clothing generally uses external power supplies. As long as the electricity is constantly powered, it can be heated for a long time. It is very suitable for people who work outdoors for a long time in severe cold outdoors. Commercially available electric heating clothing is generally powered by a small power bank, with a small voltage and relatively safer. Consumers mainly pay attention to the fact that the electric heating fibers should not bend or fold, resulting in local overheating and scalding.
Electric heating clothing lasts longer and is very suitable for workers outdoors for long periods of time in cold weather. Gallery copyright pictures, reprinted without authorization
03
How to clean self-heating clothing?
hygroscopic heating fibers will not be affected after daily cleaning, so they can be cleaned normally. However, since the fabrics of hygroscopic heating underwear are often made of a variety of fibers, including hygroscopic heating fibers, some fabrics also adopt special weaving processes. It is recommended to wash gently in warm water during cleaning, avoid using high-temperature water and hard rubbing, and avoid exposure to the sun. It is generally not recommended to use water washing for electrical heating clothing. Water washing will cause damage to electrical heating fibers or heating units, reducing the heating effect or posing safety hazards. Finally, let’s summarize, although qualified “self-heating” underwear cannot really heat up out of thin air, it will indeed be warmer to wear. You can choose as needed when buying it and give priority to purchasing products that meet industry standards.
Reference materials: [1] Xiao Xueliang, Chen Tianjiao, Xie Yuntao, et al. Development and application of heating clothing fabrics [J]. Journal of Clothing, 2021.
Author | Song Lidan Consulting Engineer Review of the Industrial Research Department of China Textile Construction Planning Institute | Zhang Jie Chief Engineer of China Textile Construction Planning Institute
(Scientific Rumor Refutation)
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