Short answer: thermal underwear is worn over base layer underwear, not on bare skin. Base layer underwear is the first layer: it is thinner and lighter, contacts the skin, and wicks away moisture. Thermal underwear is worn over it, and its job is to keep you warm.
A regular T-shirt is not suitable for this outfit. Especially a cotton one. It quickly absorbs moisture, takes longer to dry, and becomes an unnecessary layer between the body and the functional fabric. Nothing with short sleeves should be worn under base layer underwear; this is important. But there are nuances. Because clothing for a few hours in the city and an outfit for active movement in the cold are different tasks.
Why thermal underwear is not worn on bare skin
Thermal underwear is the first layer in the dressing system together with base layer underwear. Base layer underwear is thinner and lighter, lies closest to the skin, and wicks away moisture, while thermal underwear is worn over it and is responsible for warmth. It is important what happens with moisture when you move. Climbing a mountain, working with equipment, a long hike, activity outdoors - the body starts to produce more heat and sweat. If moisture remains near the skin, it becomes cold after a decrease in activity. And very quickly. When the fabric of the base layer underwear fits the body, it is easier for it to do its job. Therefore, you should not add another regular T-shirt under the base layer underwear just "for warmth".
It will not always be warmer from this. But the dressing system will work worse.
There is a small clarification: the two-layer outfit should fit comfortably. Excess thick items should not bunch up under it, otherwise they will interfere with the fit.
What happens if you wear a T-shirt under base layer underwear
It all depends on the T-shirt. With cotton, the scheme is simple. During activity, it absorbs sweat. The base layer underwear ends up not near the skin, but over the wet fabric, so it cannot properly wick away moisture. When the pace drops or you go out into the cold, comfort also drops. For a walk from home to the car, this is unlikely to be a problem. For a few hours of activity outdoors - it already can be.
A thin synthetic T-shirt is also capable of wicking away moisture, but you end up with two layers with the same task, and the base layer underwear under the T-shirt works worse. Therefore, a T-shirt is not worn under base layer underwear: nothing with short sleeves should be under it.
Can you wear a T-shirt under base layer underwear
No. Base layer underwear should fit the skin, and nothing with short sleeves can be worn under it: this disrupts moisture wicking. Even in the city, where you often enter buildings, it is better to take off the outer layer and stay in thermal underwear than to add a T-shirt under the base layer underwear. If a specific fabric causes discomfort, it is more logical to check another material or model of base layer underwear than to add a T-shirt.
For long trips, it is more convenient to take a spare set of base layer underwear: it is easier to replace it during the day. Here you already need to look at the activity, temperature, and the possibility of changing clothes.
The main rule is simple: an additional layer should solve a specific task, not just be another layer.
How to properly wear thermal underwear in layers
More clothing does not mean more comfort. It is much more important that each layer does its job. The basic scheme looks like this:
- first layer - base layer underwear and thermal underwear: base layer underwear wicks away moisture, and thermal underwear keeps you warm;
- middle layer - additional warmth: fleece, a sweater, or other clothing depending on the temperature and activity;
- outer layer - protection: jacket, softshell, membrane clothing, or another solution for wind and precipitation.
And here it is easy to see why a regular T-shirt under base layer underwear is not needed. It does not add a new function to the system. It is much more useful to correctly choose the second or outer layer.
Thermal underwear should not hang on the body
The fit also matters. The first layer should fit the body, but not constrict it. If the sweater hangs in folds, and there is constantly a large air gap between the fabric and the skin, moisture wicking works less effectively. The other extreme is an outfit that makes it difficult to sit normally, raise your arms, or spend a few hours in motion. It is easy to check. Put on the thermal underwear, lean over, sit down, stretch your arms forward. Nothing should pull at the shoulders, waist, or under the knees.
Choosing an outfit online and hesitating between two sizes? It is better to clarify the parameters with the manager than to take it at random.
Different solutions are needed for service, hiking, and the city
The question "which thermal underwear is warmer?" does not always help with the choice. It is more useful to start with something else: what will you be doing in it?
At high activity, it is important that the base layer underwear works properly with moisture. If a person moves a lot, a too warm outfit can create more problems than benefits. First you sweat, then you stop - and it becomes cold. For less active tasks in the cold, a different balance is already needed. Here thermal insulation comes to the forefront. In the city, the scenario changes again. The street, transport, office, store, car - the temperature constantly jumps. Thermal underwear should be comfortable not only in the cold, but also when you enter a warm room for twenty minutes.
Therefore, at Camotec, we recommend basing it not on a single temperature indicator, but on the entire task: level of activity, weather, duration of time spent outdoors, and other layers of clothing.
What to wear over thermal underwear
There is no single outfit for the whole season. In cool weather, a fleece sweater or jacket over thermal underwear may be enough. When it is colder - an additional insulating layer is added. If there is wind or precipitation - appropriate outer protection is needed. Sometimes people try to compensate for incorrectly chosen layers with thick thermal underwear. It does not always work. If the jacket lets wind through from above, another warm sweater under it does not solve the problem as effectively as a proper outer layer.
Thermal underwear is part of a system, not a magic suit against the cold.
So what to wear under thermal underwear?
Base layer underwear is worn under thermal underwear: it wicks away moisture and works as the first layer together with thermal underwear. Thermal underwear is not worn on bare skin, and a T-shirt under base layer underwear is not suitable.
Choosing thermal underwear for service, the city, or active recreation? First, determine the task.
In the Camotec catalog, there is men's thermal underwear and women's thermal underwear, as well as all thermal underwear for your activity level and dressing system. If you are not sure about the model or size - write to the manager and indicate your parameters and conditions of use. This will make the choice easier.
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