Choosing thermal underwear begins with determining your needs, goals and capabilities.

Thermal underwear is underwear designed to maintain the body's microclimate while removing excess moisture. It also has significant breathability properties. With the correct selection of this type of underwear, you will be comfortable at any temperature: warm on a cold day, and comfortable on a hot day. Two main criteria are thermal insulation and the ability to remove excess moisture from the body .

For summer, the main criterion is moisture removal, for winter - thermal insulation. In any case, it is important to keep your body dry - this is for your comfort and health!

There are all kinds of thermal underwear models - blouses, turtlenecks and T-shirts, various long johns and pants, shorts, breeches, suits, overalls, as well as socks, gloves, and even hats.

First of all, it is divided into sportswear, for active recreation, and also into models for daily wear. Requirements for quality characteristics and price increase in proportion to the activity of use.

According to weather conditions: for cold or hot weather.

Summer thermal underwear It should be thin, light, protect from overheating and possible hypothermia (when changing from active movement to a passive state, for example, when playing sports), remove excess moisture! This is 100% synthetic, if the underwear is chosen for active sports, or composite fabrics, with the addition of cotton and linen, for less active physical activity.

For cold times the underwear should be warm. At the same time, each manufacturer has a division for cool, cold and very cold weather. The rule is that the thicker, the warmer.

Material composition and main characteristics

Both synthetic and natural materials are used for thermal underwear. Cotton and wool are familiar to us, but they are significantly inferior to synthetic materials, especially polypropylene, as well as polyester and their derivatives. Cotton absorbs moisture many times more, retaining it for a long time, and dries more slowly. Most of all, it is suitable for daily wear with minimal activity. If you choose wool, then the highest quality and warmest is merino wool. Underwear with this composition is suitable for low activity and very cold temperatures: most often for everyday wear or outdoor activities, such as fishing.

In order for this underwear to work, it requires contact with the skin and the creation of an air cushion.

The second layer is designed to increase thermal properties or to protect against external factors (wind, moisture).

Most thermal underwear fabrics are made from microfibers, which makes the fabric thin and pleasant to the body. Sometimes lycra and elastane are added, more often for underwear designed for active movement. They increase the comfort of movement, and the tight-fitting cut helps to avoid deformation during long-term wear, which is especially typical for natural fabrics. Antibacterial impregnations or silver fibers are also added.

Sports-type thermal underwear primarily designed for moisture management and breathability. During active exercise, there is no need for warming. All sports thermal underwear is made only from synthetic fabrics; for warmth, a second layer or membrane clothing is used - in cold times - or simply sports outerwear with a membrane that already includes the functions of thermal underwear.

Hybrid thermal underwear(for active recreation and just country walks) should be composite to maintain thermal insulation and moisture removal: single-component or two-layer. In two-layer thermal underwear, the first layer removes moisture, the second is responsible for thermoregulation and removal of moisture further - or its evaporation. The second layer resembles cells in which there are air molecules heated by the body, which are responsible for the further removal of the body’s vapor moisture to the next layer, or for its retention and drying due to body heat.

The first and second layers of thermal underwear. Companies produce two types of underwear. The first layer is worn directly on the naked body. Thermal underwear of the second layer resembles a tracksuit and can be used in the autumn-spring period as outerwear. Most often from fleece of varying density, or from a combination of fabrics: the inner layer is fleece, the outer layer is synthetic material: polyester, polyamide, nylon, etc.; it can have a sprayed membrane (PU) or consist of membrane fabric (the ending in the name of the material is TEX).

Choice

When you have decided on the style, temperature conditions and the activity of your movements, proceed to the choice. There are specialized brands for sports and outdoor activities, as well as manufacturers of “outdoor” clothing - for active and everyday wear.
Pay attention to the anatomical cut - for maximum comfort - and to the seams.

Care

Read product labels carefully. General recommendations are:
. Gentle hand or delicate machine wash without drying 30-40 C.
The use of specialized detergents for synthetics or sportswear is advisable; the use of softeners and antistatic agents is possible if there are no such restrictions.
. Do not use chlorine-containing or other bleaches or aggressive detergents.
. Do not iron, do not expose to overheating (drying on hot surfaces, such as a central heating radiator).
. Thermal underwear with a fleecy inner layer should be washed inside out.
. It is advisable not to wring or twist, but to dry flat.

The correct example opinion

Thermal underwear is designed to always be comfortable and pleasant to wear. Allows you to keep your body warm and dry with a minimum of clothing. Ideal rule: 1 layer in summer, 2 layers in the off-season, up to 3 layers in winter (thermal underwear of the first layer and outerwear for average negative temperatures or 3 layers for very cold temperatures: first and second layers of thermal underwear and outerwear).

That's why:
. choose the right thermal underwear depending on your physical activity and climate conditions. When choosing thermal underwear for sports, pay attention to the specialization of the manufacturer (thermal underwear for diving will never have the same functional characteristics as mountaineering);
. do not wear too much warm outerwear;
. thermal underwear for cold and very cold conditions is most effective when combined with outerwear with moisture- and windproof properties;
. Do not wear regular clothes made from natural materials under the second layer of thermal underwear!
. Do not wear cotton or linen sweaters over the first layer of thermal underwear!

And don’t forget, quality things cannot be cheap. Don’t chase design and fashion, choose convenient and comfortable things.

Previously, I already told you about the principle of multi-layering, which is promoted by many outerwear manufacturers. Today I want to continue my story and dwell in more detail on the base (body) layer. What is thermal underwear? Why do children need it? What happens? And is it possible to do without it? These questions come to mind for everyone who is faced with a choice for the first time.

What is a base layer?

As the name suggests, a base layer is the first layer of clothing you put on your baby's naked body. Its main function is to keep the child dry. Previously, cotton was considered the ideal base layer, but cotton has one significant disadvantage - it absorbs moisture and no membrane overalls can cope with removing moisture from a child’s body. As a result, if a child, sweaty from activity, decides to sit and rest, then he risks freezing and getting sick.

What types of thermal underwear are there?

Now many manufacturers offer synthetic thermal underwear, saying that specially treated materials instantly allow moisture to pass through and remove it further from the body. This is true, and synthetic thermal underwear copes with this task perfectly, but it is more suitable for athletes than for children. And there are several reasons for this: synthetics can cause allergic reactions on the delicate skin of a child, which is especially important for the little ones, and another significant drawback: synthetic thermal underwear does not warm.

The second, and in my opinion, the best option is woolen thermal underwear. It is great for children of any age because:

• consists of 100% natural materials
• hypoallergenic
• does not absorb moisture, but removes it from the body
• provides extra warmth

Merino wool

High-quality thermal underwear is made from Merino sheep wool, which in itself is a great find. This wool is much thinner and softer than ordinary wool, does not cause allergies, does not prick and is pleasant to the body.

Due to the large number of air pockets, products made from such wool are very light but at the same time provide excellent warmth.

For older children, synthetic materials are sometimes added to wool, especially for socks and tights. Synthetics increase durability and increase moisture wicking ability. This type of thermal underwear is called hybrid or combined and is great for active children.

How to wear thermal underwear?

1. Choose a model by size. Thermal underwear must fit the body tightly enough, otherwise it simply will not be able to perform its functions. Therefore, the principle of taking for growth does not apply here. The only exception may be babies up to a year old; they can take thermal underwear with a reserve.
2. No T-shirts! Very often, I hear the question: can I wear a T-shirt and tights? No you can not. A T-shirt and tights will absorb all the moisture if the child sweats and thermal underwear will no longer help.
3. Dress appropriately for the weather. Thermal underwear is not a panacea and, depending on the weather, you may also need an intermediate layer that will provide additional warmth in the coldest weather. The middle layer should also be synthetic (fleece) or wool to continue the work of the thermal underwear and wick moisture away from the child's body.

By following these simple rules, you can easily choose thermal underwear for your child, especially since we have already

In order to feel comfortable at low temperatures, you need to dress according to the rules of the layer concept. Layer-by-layer concept - includes three layers of clothing: the first - thermal underwear, the insulating second layer, and the last, third - protective, that is, an outer winter fishing suit.

Today we'll talk about the first two layers. The main thing is to always remember that it is not the amount of clothing that provides reliable thermal protection, but its correct selection! The body of a person engaged in active recreation, including fishing, works intensively during his favorite activity. The fisherman needs to get to the fishing spot, often for this he has to use public transport, on a pond, in deep snow, reach the fishing spot, drill a large number of holes in the ice during fishing and, of course, return home. In this case, a large amount of energy is expended with the release of moisture - sweat. Moisture prevents heat retention in clothing, so all layers of clothing should not absorb and retain it, but quickly release it out into the atmosphere. Oddly enough, only synthetics can handle this well. Natural materials: cotton and wool absorb moisture well, but they also “part with it” very reluctantly.

THERMAL UNDERWEAR

First layer of clothing- thermal underwear, must be worn on a naked body. The best solution is to put on thin thermal underwear first. The main purpose of thin underwear is to remove moisture from the human body as quickly as possible. Under no circumstances should you wear cotton underwear under thermal underwear! Such fabric will quickly become saturated with moisture: the angler will even feel hot while moving, but when he starts fishing while sitting on a fishing box, his activity will sharply decrease and he will immediately feel cold, even with slight frost. Then, over thin thermal underwear, thick ones are put on. As already mentioned, for people with high physical activity, this layer of clothing is made only from synthetic fibers. In mild frost, you can limit yourself to only one thin or thick thermal underwear. All this depends on the individual characteristics of the fisherman. In any case, if the angler sweats, then within a very short time, excess moisture will be removed from the body into the outer layers of clothing, and then into the atmosphere. The skin and thermal underwear will remain dry, and heat will continue to accumulate in the clothes.

With less active physical activity, natural materials can be introduced into the fabric, and with very low activity, in the composition of thermal underwear, the wool content can reach up to 100%. But, such thermal underwear is only suitable for older people who are usually inactive outdoors.

The RYBOLOV-SERVICE company's assortment includes a wide range of thermal underwear and insulated clothing. This clothing is made of polyester and is recommended for leisure activities ranging from low to high. It “breathes” well, removes moisture from the body, accumulates heat, is comfortable to wear and can be machine washed in a gentle cycle.

Hi all! We continue to talk about modern clothing.

Today we’re going to look into thermal underwear and choose a set for ourselves.

THERMAL UNDERWEAR 1 LAYER

Let's start with the 1st layer of linen. It is used in summer and during high physical activity. The main purpose is to remove moisture and coolingbodies. And here the key point is the material from which the underwear is made.

Now there will be some complicated terminology.Important parameters for thermal underwear are the affinity for moisture of the underwear material (degree of hydrophilicity). It affects the rate of water transfer to the next layer and the wettability of water, and therefore the rate of moisture evaporation. If we arrange common thermal underwear materials according to increasing degree of affinity for moisture (degree of hydrophilicity), we will get the following series: polypropylene, polyester, polyamide (aka nylon), wool, cotton. From the point of view of the basic slogan - they say, the function of thermal underwear is to remove liquid moisture into the next layer, the best option would be polypropylene underwear, but in practice this is not always the case. Most of the moisture released through the skin is excreted in liquid form through the channels of the sweat glands. Increased sweating, as a rule, is evidence that heat production exceeds heat loss and the body, by secreting sweat, tries to cool itself due to the evaporation of moisture from the surface of the skin. Thermal underwear can interfere with this process by removing moisture before it evaporates into the next layer. That is, the body practically does not cool down and the body continues to secrete sweat. Thus, it is much more expedient to have thermal underwear that can evaporate the maximum amount of moisture from its internal and, to a lesser extent, external surface and thereby further cool the body, and such thermal underwear must be more or less hydrophilic.

In general... I don’t recommend buying polypropylene thermal underwear. Choosing underwear frompolyester and polyamide (nylon). Cotton, wool, and mixed fabric underwear are more suitable for low activity and are not as versatile, so I don’t recommend buying them either.

So what options are there on the market?Very good. Consists of 100% polyester, costs less than 1000 rubles per set. The best option in the lower price segment.

A rather serious disadvantage of synthetic underwear compared to cotton is that bacteria begin to multiply there very quickly, literally after one day of wear. This threatens not only an unpleasant odor, but also skin irritation. For the torso this is not so critical. But a rubbed butt is not the best thing that can happen to you during a field trip. Fortunately, thermal underwear manufacturers have solved this problem too, using all kinds of impregnations and adding silver, bamboo fiber and other materials to the fabric structure. At the same time, impregnations are very short-lived, but bamboo fiber and silver work as they should.

Those. We come to the conclusion that in addition to thermal underwear, we also need thermal underpants with antibacterial properties, which we use constantly and, if necessary, wear long johns over them. (Let's call it a zero layer, or everyday thermal underwear)The best option I found for a reasonable price is .They are one-third made of bamboo fiber, they wick moisture away well, and are pleasant on the body even in everyday wear. I recommend!

You can also complement the set with thermal T-shirts for everyday wear. But they must also have antibacterial properties.

Often, to improve the evaporative function of thermal underwear, a more complex structure of its material is used. The two most famous technologies are Polartec ® PowerDry and CoolMax. PowerDry underwear will cost twice as much, but evaporates moisture about 20% faster.

Thermal underwear made from CoolMax works even more effectively, but is not yet produced in Russia (or I just don’t know about it). So the price tags are not encouraging - from 4000 per set.

An even cooler technology is combined zone underwear. A prominent representative is X-Bionic thermal underwear. Such thermal underwear redistributes heat from the areas where the greatest amount of heat is generated to areas that are always cold - the lower back, shoulders, elbows, knees. Sweat is also removed from the areas of its greatest production in the so-called. evaporation zones.

Another advantage of X-Bionic thermal underwear is that it also performs a compression function. Muscles contract in certain places, which keeps them toned, improves blood circulation, and you get less tired. And in the area of ​​elbows and knees, thermal underwear acts as supports. Joints are also less tired! Naturally, such a magnificent thing cannot be cheap - the price for a set starts from 15,000 rubles. This is truly a tool for professionals.

THERMAL UNDERWEAR 2 LAYERS

The first layer is more or less dealt with. I tried to give the best options in terms of price/quality in each price category. Let's now select the 2nd layer underwear. It is made from fleece and similar materials. The purpose of such underwear is to remove moisture from the body, as well as some thermal insulation, at the level of a thin fleece jacket. It can be used both on a naked body (with moderate sweating) and in conjunction with layer 1 thermal underwear (with heavy sweating, for example while jogging).

With all the variety of products offered, there are only 2-3 working options on the market.In the lower price segment it is about 1600 rubles per set.Excellently removes moisture and dries quickly.

Analogues from other Russian companies (Splav, Garsing, Ana-tactics and Giena) are still inferior to army underwear in terms of price/quality.

If you need something more effective, look for underwear with a tagPolartec PowerStretch. This fleece material has a more complex structure, so it evaporates moisture from the body faster. In addition, PowerStretch underwear is pleasant on the body, which cannot be said about VKBO underwear. Another feature is that the material has a dense fabric layer on top, which makes the clothes very durable and even provides some protection from the wind.

Of the Russian companies, products from PowerStretch are offered by the Splav company. Don't let the kit's high price tag scare you. Power Streth is worth the money, and will last twice as long as VKBO underwear.

I don’t see much point in choosing something more expensive and cooler from clothing from Western companies. The key role here is played by the material of manufacture. Sewing such clothes is not difficult, and its quality is approximately the same for everyone.

RESULTS.

The result was a fairly large set of underwear: two thermal underpants made of antibacterial materials, 1-2 sets of thin underwear for warm weather, and a set of insulated fleece underwear. This set is very versatile and will help you stay dry in any situation.

Perhaps I will remind you again that thermal underwear should fit snugly to the body. Most often, weakness occurs in the lower back area, which is why sweat in this area collects in droplets and rolls down. Because of such a trifle, comfort drops greatly. It makes sense to take the linen to a tailor and have it sewn up.

That's all for now. In the next part we will look at the middle insulating layer.

This article is not about the choice of underlayers, but about the relationship between thermal underwear and thermoregulation. The theory on which practice and our well-being on the route is based.

Before we begin to disassemble the thermal underwear itself, let’s take an excursion into distant distances, where we will try to understand something about the thermoregulation of the human body. After all, this has a lot to do with thermal underwear. Although, of course, it is much easier to believe the lines written on the websites of some manufacturers “we produce the best thermal underwear in the world” and then click the mouse, adding it to the cart, nevertheless, we do not forget that theoretical training in this matter adequate to our hikes is also needed .

So, thermoregulation. What is it and what is it eaten with? Thermoregulation is the body's ability to maintain body temperature within certain limits, regardless of the external temperature. If we are cold, then the body, due to the biochemical processes occurring in it, tends to increase the temperature, and if we are hot, then, on the contrary, to cool it down.

Thermoregulation is one of the processes of homeostasis, a dynamic state of equilibrium between the internal environment of the body and its external, often aggressive, environment. In relation to body temperature, homeostasis is a clear example of negative feedback. Our body, having received a signal about hypothermia or overheating, immediately tries to change the direction vector of the process to the exact opposite. This is the key to the effectiveness of thermoregulation. Unfortunately, it is possible for a person to create positive feedback, on the contrary, only increasing the impact of the external environment. Vivid examples in this case are drinking alcohol “to warm up” and the wrong choice of clothing. Under such conditions, the system has a destabilizing effect and homeostasis - self-regulation of the body - either does not occur as a process, or its effectiveness is insufficient and the impact of temperature factors on the body becomes threatening or critical.

Often tourists, talking about thermoregulation and adaptability to temperatures (especially low ones), identify people with animals. This is far from correct. Despite the external anatomical similarity and the myths that come from nowhere that the body of one or another animal is almost one hundred percent close to humans, absolutely each type of animal has its own biochemical world and processes such as the same thermoregulation occur in each of them. them in their own way. One example is sweating, which in humans is the main means of combating overheating and, in general, one of the components of thermoregulation, an instrument of homeostasis. But the same pig does not have the function of sweating in the body, although it would seem that it also has no hair. During its evolution, each species of mammal has developed its own mechanism of thermoregulation, which can be carried out at the level of nervous and/or humoral (through liquid media - blood, lymph, tissue fluid, etc.) activity, metabolism, energy metabolism and even the behavior of the animal. As a result, for each species we have different body temperatures, different limits of body temperatures at which life is preserved. If the Arctic fox has a constant body temperature of +39, then in some species of bats the body temperature can range from -7.5 degrees to +48.5. Naturally, such variations require a radical difference in the processes and tools of thermoregulation.

At the same time, it should not be assumed that humans, as a species, have the same process of thermoregulation for all of their representatives. This is also very untrue. Evolution, even in the still short period of human existence, has made it possible, depending on the region of residence, to change some of the internal biochemical characteristics of the aborigines. For example, the indigenous inhabitants of polar latitudes are characterized by the following evolutionary adaptations:
- high body density;
- relatively high musculoskeletal mass;
- a strong skeleton with an increased gamma-globulin fraction of blood serum;
- developed immune system;
- high ventilation capacity of the lungs;
- increased hemoglobin content in the blood;
- high degree of fat oxidation;
- high intensity of energy processes;
- high stability of the metabolic rate in any conditions;
- large filling of body tissues with blood and its much more intense circulation than in other representatives of the species;
- increased heat production;
- weak sensitivity of the skin of the hands and face to temperature stimuli;
- extremely low variability of adaptive adaptations and their high heredity.
As a result, we see significant differences from a “common” person, although the external differences are small. The mixing of different peoples over time gives rise to some differences in thermoregulation even among modern urban residents. Some freeze more, some less, some acclimatize perfectly to almost any conditions, while others are able to survive only at room temperature. Despite the fact that to a large extent we kill correct thermoregulation in our body ourselves, with our lifestyle, part of its processes is inherent in us genetically.

Now let's return to thermal underwear. Everything written above can now be reduced to two axioms that must be firmly understood.

Axiom 1. Thermal underwear is a thermoregulation tool for our body, allowing us to expand the body’s capabilities and increase the stability of homeostasis. Explanation: Properly selected thermal underwear will allow you to maintain a more constant body temperature. Subsequently, this will be expressed in energy saving by the body. Due to lower costs for thermoregulation, our adaptive capabilities will increase. The accumulation of cold fatigue will be delayed and endurance on the route will increase, since to some extent it is related to the body temperature limit at which overheating is felt - and the right thermal underwear will remove some of the heat into the outer layers of clothing. Since we will feel less cold at rest stops, we will rest more efficiently. Your sleep will also be more restful and healthy. As a result, having a small impact on each element, on each component, we get a tangible total effect in relation to a long hike.

Axiom 2. All the advantages of thermal underwear, provided they are chosen correctly, are noticeable only if our body functions correctly in terms of thermoregulation. Otherwise, there will either be no effect or it will be minimal. It is very important. In the modern world, many thermoregulation tools in humans work with much less efficiency than what is inherent in nature. This is due both to the lifestyle to which the body adapts and hides the necessary tools away, and to the state of health. Our body must react correctly to changes in external temperature, i.e. thermal underwear is a secondary factor, not a primary one.

Now let's talk about the types and properties of thermal underwear.
Typically, thermal underwear for tourists is divided into layers, the first layer and the second. This is a rather arbitrary division and it serves, first of all, to simplify the combination of layers of clothing for a particular route.

Thermal underwear of the first layer is usually thin, tight-fitting underwear. It should wick moisture away from the body. How simple it is to say, right? Withdraw. How does it take away?

With excessive physical activity, the body releases a lot of sweat and heat to the surface of the skin. The purpose of the first layer of thermal underwear is to absorb sweat as little as possible and not interfere with the passage of vapors through its fabric. In this case, it actually “removes” moisture from the body and the body cools better.

But there is a nuance associated with the peculiarities of human thermoregulation. If outerwear is no longer thermal underwear, but clothing that is too thick, then in the area between layers of clothing with intense sweating the temperature increases and, at the same time, it becomes saturated with moisture. In this case, the surface of the skin becomes covered with profuse sweat, since the evaporation of moisture from its surface under such conditions stops - as in a bathhouse. As a result, clothes, like thermal underwear, simply become wet with all the ensuing consequences. And the consequences here are intense heat transfer from the body to the external environment almost directly and the risk of hypothermia, both general and local. As a conclusion, clothes on the route should not be too warm for the given conditions, plus excess heat should always be released through ventilation or simply by opening the zipper slightly.

So, removing moisture from the body eliminates overheating and reduces the likelihood of subsequent hypothermia. That is, eliminate peak surges in the process of thermoregulation.

Thin thermal underwear can provide warmth. No, not by itself, of course. Only as an attempt to deceive the second law of thermodynamics. And this also needs to be discussed in more detail.

Man and the environment are, from the outside, parts of one general system, and this dictates certain physical laws that they must obey. In particular, one of these laws is the transfer of thermal energy from one object to another. As a rule, the environment is colder than the human body, and in order to achieve thermodynamic equilibrium, it is necessary to transfer excess heat to the environment and equalize the temperatures. A person's clothing should try to correct this injustice. By itself, thin underwear can only reduce heat loss through convection, and even then only with a small temperature difference. But when combining thermal underwear of the first and second layers on a route in severe winter, the decrease in heat transfer intensity is quite large, especially when a person sweats intensely and freely, while the thermal underwear of the first layer remains relatively dry (since it freely passes steam through itself), and the second, although wet, it does not come into contact with the skin and maintains thermoregulation until it is completely saturated with moisture (this should be avoided by tourists at all costs).

And the last thing about thermal underwear of the first layer - it should not cause skin irritation. Otherwise, dilation of blood vessels in the allergy sites is possible, which will lead to increased heat transfer and failure of the thermoregulation system.

Now about the thermal underwear of the second layer. This underwear is made from different fabrics than the first layer and has a more “fluffy” structure. A stationary or low-moving heat-insulating layer of air is formed inside the fibers of the laundry. Due to this, underwear from the same Polartec High Loft provides excellent warmth, which thin thermal underwear of the first layer cannot.

At relatively low ambient temperatures and low-intensity physical activity, it is quite possible to use only thermal underwear of the second layer. It will warm perfectly as long as it copes with the removal of moisture from the surface of the skin. But, due to its “fluffiness”, sooner or later it will get wet. It should be taken into account that the laundry is usually not completely saturated with moisture. That is, we walk, and it warms us, although we feel wet from sweat. But then we throw the backpack off our shoulders and a fresh breeze blows across our backs. And why? Because there was no intermediate layer, not saturated with moisture, between the insulating thermal underwear and the skin. As a result, the water in it instantly cooled under the influence of the cold wind and came into contact with the hot body. The heat transfer in this place increased by an order of magnitude and the next day we were cramped - like “blown out”. Well, you understand, you need to dress correctly.

What if you use only the first layer, without the second? In this case, the layer between the first layer and outer clothing will disappear, due to which moisture will be removed directly to the latter. In the winter season, this will be fraught with rapid freezing along the route due to icing of outer clothing.

A special case can be considered the situation in the warm season, when thermal underwear allows you to better cool the body. The second law of thermodynamics will again try to transfer excess, in his opinion, heat from the environment to the body and thermal underwear will play the role of a protective layer. In this case, linen of both the first and second layers can be used. The second layer will become wet from sweat and because of this it will better cool the body. Naturally, this applies to low-intensity physical activity, since in this case the second layer will lead to overheating, but the first layer, on the contrary, will allow for better cooling.

This is the theory that came out. As usual and always, what exactly to buy and use is up to you.