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How to choose thermal underwear for hiking and climbing


This article is for those who are just beginning their hiking life and have not yet had time to get everything they need. Many people starting to hike for long periods today do so by using the services of companies that organize hikes and climbs around the world for beginners. This way, safety is ensured and no unnecessary and expensive time is spent on organizing.

In such cases, the packing for a hike, as a rule, carried out by the provided list of clothing and equipment. Some things on your first trips make sense to rent, while others should be purchased immediately. First and foremost, you should probably buy trekking shoes and overalls. In almost any list of equipment in a serious hike – wherever you’re going – in the summer or winter, will be an item of “underwear.

Few myths, opinions and unreasonable expectations exist for any type of clothing as much as for thermal underwear.

What is thermal underwear?

Many novice hikers and climbers are misled by the very name “thermal underwear”. They think that the main function of clothing with this name – to keep warm. Myths are born about how good thermal underwear is not afraid of any frost. This is not true. Somewhat more accurately reflects the functionality of the garment layer another name – “functional underwear. The main function is the REMOVAL of WATER FROM THE BODY .Only for underwear designed for sedentary time spent in cold conditions is moisture evacuation an auxiliary function, and warming is the main function. This is primarily clothing for winter fishing and ambush hunting. For active tourism, mountaineering, travel it is the removal of moisture from the body is the primary task of the garment layer.

The fact that sweat, lingering near the body, leads to increased moisture in clothing and significantly increases the body’s heat loss. In a strong wind, wet clothing further contributes to hypothermia (hypothermia) of the body. That’s why it is often not necessary to put on a pile of warm clothes, in order not to get cold, it is enough to wear thermal underwear and wind protection (if the wind blows).

Как выбрать термобелье для походов и восхождений

How thermal underwear works?

The inner surface of the thermal underwear is in maximum contact with the skin and due to its properties effectively and quickly absorbs the released moisture. There is no special magic here – for the system to start working, a layer of moisture must form between the surface of the body and the inner layer of the underwear, which will tend to the space with less moisture – outside.

It is important that the material itself does not absorb moisture, but only transports it outward, otherwise the effect of cooling by wet clothing occurs, which is extremely undesirable. The exception is clothing made of natural wool, which absorbs some moisture inside the fibers, while the outer part of the fiber in contact with the body has hydrophobic properties and practically does not cause the effect of unpleasant cooling.

The next step in the operation of thermal underwear is the evaporation of moisture from the outer layer of the material to the outside – to the air or to the upper layers of the garment. The transport of moisture from the inner to the outer layer of fabric occurs mainly due to the so-called capillary effect, known to us from biology classes. And for the moisture to evaporate quickly, it requires the maximum surface area of the upper layer of the fabric, which is achieved by using different fibers than on the inner layer. The “loose” structure of the material multiplies its surface area, and thus the efficiency of evaporation. Of course, to make the fairy tale come true, it is necessary to use real thermal underwear, not substitutes.

Thermal underwear is a team player

Now it is quite obvious to us that “thermal underwear” actually warms up no more than any other clothing of the same density and composition. The super effect is achieved not by the insulating properties of the material, but by its ability to leave the body dry during physical exertion. This means that the more you move and (or) the more varied the schedule of your motor activity (then standing, then moving intensively), the more useful the thermal underwear will be. At night in a sleeping bag it is not so much the thermal underwear that keeps you warm, but the sleeping bag itself and the “placebo” effect. Many people just enjoy the feeling of being snug against their body.

In cold weather other layers are put on top of the first, and the proper effect of dry and warm body can only be achieved by team play. The second layer, when actively moving in cold weather, should pass the moisture away from the body easily, without trapping (not absorbing) it. The best way to do this are materials such as fleece and softshell. They stay dry, which means they’ll keep you perfectly warm. If your movement takes place in the rain or wind, you need another third, protective layer of clothing, worn over the first two. It should preferably be made of a material with a good membrane, which will have a selective permeability – to breathe on the inside, and not let the wind and rainfall outside. The higher the breathability characteristics of the membrane, the less moisture drained from the body will accumulate on its inner surface. Remember these simple principles of clothing selection.

Thermal underwear (functional underwear) and underwear

Nowadays, an incredible number of manufacturers produce “something” called “thermal underwear”. Many manufacturers do not think much about functionality, often just imitating well-known manufacturers. Supplying the consumer with goods of dubious suitability, they take advantage of the fact that, in fact, there is no specific distinction drawing a clear line between “underwear” and just “underwear”. If functionality and safety are important to you – there is only one working recipe “with a guarantee” – buying products from reputable manufacturers from trustworthy places. Why should we recommend doing this? Let’s break it down.

QUALITY AND DURABILITY are ensured by the use of proper materials and quality control. It’s no secret that the vast majority of light industry products are now sewn in Asia, mostly in China and, a small number, in other not very developed countries. “China” has long ceased to be synonymous with poor quality products, everyone knows that “China is China. Underwear for active wear is subjected to very high loads, frequent washings. The difference in service life of quality and low-quality underwear can be very significant, and the initial savings in purchase cost over time will not be so obvious. Even more important is that when using low-quality materials will suffer

FUNCTIONALITY, which is what makes the purchase of thermal underwear meaningful decision. Renowned manufacturers are conducting research, gradually increasing the functionality of thermal underwear. Technology of sewing and weaving fabrics, the structure of the fibers do not stand still. Of course, in any case you are not insured against aggressive marketing of advertisers, who often embellish the achievements of engineers and wishful thinking, but nevertheless. Underwear gets better. Since the beginning of the evolution of thermal underwear, it has been “taught” in one way or another:

SAFETY. Most types of thermal underwear for sports activities are partially or completely made of synthetic materials. This thermal underwear has maximum contact with the skin of the wearer. It is very important not to provoke an allergic skin reaction, which in difficult conditions, hiking can turn into much bigger problems than in the city. Also, many types of low-quality thermal underwear is constantly electrified, which does not improve the health and feeling of comfort when using it.

Given all this, think carefully before you buy an “economy option” of an unknown manufacturer, which at first glance is “no worse”.

In this article we will consider only the models designed for active use in hiking, traveling, climbing.

Basic criteria for choosing thermal underwear

Features of usage

In contrast to sports in the city, the use of thermal underwear during hiking and travel is often associated with the need to stay in it for a long time, sometimes for several days. And the more difficult the hike or climb (e.g. Mera Peak), the more likely it is. Moreover, during such a long period, the nature of your physical activity may change considerably. When, for example, you run a mountain marathon, the load will be constantly high, and the main task of your underwear will be constant removal of moisture and heat from the body. During the twenty-four hour ascent in the mountains you will be either walking intensively uphill with a heavy backpack, or being motionless for a long time during resting places, waiting in a line on the railing, or in the evening in a bivouac. Also thermal underwear is often used as basic clothing for sleeping. Of course, in such conditions, very tight, extremely aggressively moisture-wicking model is not the best option. Also you will not suit the variant for passive recreation, made of cotton.

Thermal underwear material

First of all, let’s define – synthetic or natural materials? 

Natural thermal underwear

Despite the renewed fashion for natural materials, it is necessary to immediately exclude when choosing models made even partially from cotton or similar natural materials. Perhaps in the very near future modern technology will lead to the appearance of natural fabrics, functionally not inferior to synthetic. But at the moment, most natural materials are not suitable for the manufacture of functional underwear for outdoor activities and sports. The main disadvantage is that such materials absorb moisture well and quickly and take a very long time to dry.

A pleasant exception is wool. But not any, but only fine-wool sheep, known as merino. Merino wool is an excellent raw material for sports underwear, which by its properties is in many ways as good as the best synthetic counterparts. In addition, this wool after the first washings ceases to cause a feeling of prickly, which is associated with many such products. Wool underwear wins over synthetic underwear when used in cold conditions, and loses out slightly in conditions of maximum perspiration, because it absorbs up to 36% of moisture. It should be noted, however, that it dries rather quickly, and being wet continues to keep warm and remove excess moisture, without creating that usual “conditioner effect” for wet cotton. Also, fine wool underwear is surprisingly well behaved when worn in the heat. This is achieved, in part, by the fact that the wool thermal underwear rarely sits “flush”, as its synthetic counterparts, it is less close to the body, thus providing better air circulation near the skin. Especially wool is difficult to replace when worn for several days for a long time – it is much better to keep freshness and is completely hypoallergenic.

The main disadvantages of wool thermal underwear is its high cost and faster wear and tear compared with synthetic. Slowly dries, absorbs moisture up to 36% of the weight of the fabric, respectively, when wet, it increases in weight. It can also “shrink” when washed carelessly. May not be suitable for vegans.

Synthetic thermal underwear

Currently, synthetic underwear is the clear leader in the outdoor market. Synthetics practically does not absorb moisture (up to 0.5% of fabric weight), dries quickly, is worn for a long time, weakly stretches (changes shape over time) when worn, does not shrink, unlike wool. Also there are quite technological and at the same time very inexpensive models.

And yet synthetic has disadvantages. Firstly, there is a small number of users with very sensitive skin, for which synthetic is contraindicated. Secondly, synthetic very quickly loses its freshness, at most, by the end of the day of wear it will already emit a persistent smell of sweat. Manufacturers are constantly trying to solve this problem, in particular by including in the fabrics silver threads, which have antibacterial effect, but it does not solve the problem completely, but only slightly prolongs the time without odor, while significantly raising the price. Impregnating fabrics with silver ions or other antibacterial compounds is also a solution that is not too effective. In addition, any impregnation after a few washings ceases to work. Often labels that draw your attention to some antibacterial effect is more marketing. Partly to cope with the problem help sanitary deodorants, but be prepared to wash or smell, as to take a set of underwear for every day is unlikely to suit you.

The most popular material for synthetic underwear right now is polyester. For better elasticity a small amount of elastane or lycra is added. It should be remembered that polyester is very different – from high-tech hollow fibers of top manufacturers, to low-grade fiber of gray firms. A prime example of a high-tech polyester fiber is the coolmax fabric, which wicks away moisture well. Equipped with a silver thread, this material is labeled coolmax freshFX.

Combined materials

The thermal underwear made partly from synthetic and partly from merino wool is designed to combine the advantages of both materials. At first glance, such a solution looks like a “golden mean”, but it should not be forgotten that by combining the advantages, such fabric inherits the disadvantages of both types of materials.

Nevertheless, made of 50% synthetics and 50% wool, thermal underwear looks like a good universal option “for all occasions” for hiking. After all, a good set of functional underwear is not cheap, and to buy several highly specialized sets for different seasons and types of travel for most tourists hardly makes sense.

Zoning and compression in thermal underwear

Choosing underwear on the Internet or in an outfit center, we can see models that look like they came off the pages of a sci-fi thriller about the conquest of deep space. In the “light case” we see that the top or bottom does not look homogeneous, but has thickenings and changes in the texture of the fabric in different places corresponding to different parts of the body. This is the so-called “zoned” thermal underwear. Such a decision looks quite reasonable – because different parts of the body sweat and freeze in different ways, and require different attention. For example, it makes sense to protect the knees, elbows and shoulders with a thicker layer of bulk material, and the area under the arms and back to make the most breathable.

In more “severe” cases, thermal underwear also has the properties of compression underwear. These things look really weird – for example, men’s XL size blouse may look at first glance like clothes for a seven-year-old child. Such underwear, when worn on the body, fits it like a second skin and not only removes moisture, but also dampens muscle microvibrations, contributing to better efficiency of physical work. However, such underwear can hardly be recommended for continuous wear, it is more suitable for serious physical activities.

What for What?

As a universal thermal underwear for hiking can be recommended products known manufacturers, made entirely of synthetic fibers, or merino wool. Also a good universal material is a mixture of wool and synthetic. If you want to put an emphasis on certain weather conditions in your choice, then you should consider some factors.

DENSITY – the denser and thicker the underwear, the more it is designed for cold weather, the thinner it is, the better it will “breathe” and retain heat near the body, and therefore the best you will feel in it in hot conditions.

BELIEVING – it’s accepted that good thermal underwear should fit you like a second skin. In terms of “drying” the surface of the body from sweat secretions, this is true. But you have to admit that you don’t sweat all the time when you’re camping. Keeping your underwear a little loose in places will improve air circulation along your body and may make you feel better in hot weather. In cold weather, close-fitting underwear is also necessary only if you exert significant physical effort, causing profuse sweating.

MATERIAL – important when arranging accents. In conditions of high humidity and serious physical activity will work better synthetic. You’d also be better off choosing synthetic tight-fitting underwear if you have a high perspiration production. If your motor activity is closer to moderate, you can pay attention to wool or mixed composition, and the underwear may be a little looser. It should also be noted that the wool underwear in principle does not provide the same high level of fit as synthetic.

It is better to look at compression thermal underwear for true sportsmen, who will be able to realize its full potential and high cost. It is necessary to know that such underwear should not be worn without taking off for too long, it is not recommended to sleep in it.


If you are new to choosing sportswear, you should enlist the help of more experienced acquaintances and a sales consultant in the store. The more athletic use of underwear you will have, the tighter it should fit you. It is important not to overdo it! Woolen underwear when trying on and the first wear may slightly tingle, but you should not worry – after the first washings the underwear will be soft and will stop bothering you. As underwear for very cold conditions besides wool you can recommend sets of microfleece or thermolite. Too thick, thick thermal underwear will not be universal and you will have to use something else in summer.

The underwear will need to be washed after each wear. This is a very delicate process. Stock up on either a special liquid detergent or a delicate quality general purpose liquid detergent. Wash by hand in cool water or in a machine on a delicate setting with a minimum spin. Refer to the care pictogram. Usually there are no customary labels on thermal underwear, but all information is printed on the inside of the waistband. Underwear should not be bleached or ironed, and must not be cared for with chlorine!

Remember that the world has not yet created the perfect clothing – and underwear and membrane materials are not a panacea and do not guarantee absolute comfort, but only approach it as far as possible developers. Also, remember that what works for others will not necessarily work as well for you. Neither the seller nor a “competent” acquaintance will be able to assess the comfort of the clothes better than you, so listen not only to the opinion of more experienced people, but also to your own feelings!

Have a good choice, and see you on your way!

Author: Sergey Lakhotsky.


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