HMS
Humidity Management System
These are guidelines developed by Pajak in 2008, the main assumption of which is: each subsequent insulating layer, counting from the body, "breathes" at least as much, if not more, than the previous one.
Thermoactivity
The circulation of water vapor in layers of clothing and equipment, e.g. sleeping bags, is referred to as thermoactivity for marketing purposes. This name suggests that the products bearing it have the "ability" to change their physical parameters depending on the conditions in which they are used. Thermoactive is, for example, the c-change membrane, in which the size of the pores changes depending on the temperature and humidity. However, the same cannot be said about other items of clothing, whose task is to make natural physical phenomena limit the wearer's comfort as little as possible, and which in themselves do not have the technical "skill" to influence these phenomena.
The correct selection of layers of clothing and equipment will determine whether or not thermoactivity is selected so that, depending on our activity, we can make the most of the possibilities offered by products currently available on the market.
Where does water vapor come from in layers of clothing or equipment?
In short, from our body, which excretes it, and from the air in which it is found. The discomfort caused by the circulation of water, and in fact water vapor, can be experienced even during an ordinary walk. When we walk, everything seems to be fine, when we stop to admire the beauty of the landscape, we can feel the unpleasant cold on our backs. During a leisurely walk, the evaporating surface of our skin gives off more than a liter of water, and at rest we sweat about half a liter of it. How much water vapor or water are we able to give with our body to the thermal layers of clothing? Almost any amount, depending on the type and intensity of our effort. How big of a problem is water in the insulating layers of clothing or a camping set, especially people practicing tourism in winter know. Who tried it probably experienced the state of "too much too hot" and "too much too cold". In order to feel comfortable, we focus all our efforts on an intensive search for a balance between these two sensations.
In the conditions of winter tourism, you have often noticed a layer of ice on the inside of a rain jacket. This is the result of natural condensation of water vapor in the air under the jacket. Even in the seemingly dry environment of your own kitchen, you can experience this phenomenon. Just take a glass bottle out of the refrigerator to see how much water covers its outer walls. Condensation of water vapor from the environment takes place on the surface, at the point where the temperature difference is the greatest. The same happens on the outer layer of clothing when we move in very dense fog or in clouds, at higher altitudes.
In specific conditions, also membranes can, from our point of view, breathe in the "wrong" direction.
RDS, or Responsible Down Standard, is a certificate confirming the responsible sourcing of bird down and feathers
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What does water have to do with heat/thermal insulation?
Water has the highest heat capacity of all liquids known to man. That is why it is used as the main energy carrier in both coal and nuclear power plants. In addition, it is common. The body must manage water in such a way that by excreting it in the form of sweat, it cools down and prevents overheating or stops by limiting energy expenditure and prevents hypothermia. This is one of the physiological mechanisms of our thermoregulation.
So maybe we should go without clothes, and the body will regulate everything on its own? Unfortunately, our skin, as a result of evolution, has been deprived of thermal insulation in the form of hair, and we do not have feathers. Therefore, unlike other mammals and birds, physiological mechanisms alone are not enough for us. We need layers that insulate us thermally, i.e. those that will drain excess moisture and reduce unnecessary energy expenditure of the body.
Managing the water cycle
through the right choice of insulating layers/clothing
The most important thing for our comfort during each trip, both in summer and winter conditions, will be understanding that you should dress for the so-called. the "onion" and what tasks the individual elements (layers) of clothing and equipment have.
The closest underwear to the body
The first and closest layer to the body is underwear. In outdoor conditions, it should fulfill four tasks: transport water to subsequent layers, spread water over the largest possible surface, reduce odors, protect the skin from abrasions and damage.
The worst thing we can choose here will be cotton underwear. Although cotton has great potential in shaping the future of thermo-active clothing and fits perfectly into ecological challenges, the level of currently used technologies does not yet allow us to effectively use this potential. As a result, we have a fabric capable of absorbing huge amounts of liquid, but without the possibility of quickly and effectively draining it outside. We will feel it the most in winter, when we stop, even for a moment, after an intense march.
The best “fabric” construction available today that we can use is a two-layer knit. It has a hydrophobic layer on the inside and a hydrophilic layer on the outside.
It is a very well-thought-out construction, which, provided that the size of the underwear is correctly selected, will stop a drop of water on the skin until it is large enough to come into contact with the absorbent layer. At this point, the drop of sweat will move to the outer layer and spread it over the largest possible surface. This, in turn, will allow for rapid evaporation, and thus moving the moisture to the next layers of clothing.
At lower temperatures, we can use knitted fabrics with a higher grammage, partially acting as a thermal layer. Merino wool is a good example.
Quick underwear performance test
Unfortunately, in stores we are not always able to obtain a satisfactory amount of information about a given knitwear.
At home, we can conduct a simple performance test of thermoactive underwear. We put a drop of water on the inside of the "tested" underwear, and then we measure the resulting stain. In simple terms, the most effective will be the underwear on which we get the largest stain.
What's next?
The next layers of clothing are selected primarily so that, depending on the changing external conditions and the intensity of the effort, we have the ability to quickly change the characteristics of the clothing worn.
It is impossible to create uncompromising thermal clothing, despite the stubbornness of marketing departments. And quite seriously, the transport of water vapor and the simultaneous reduction of air movement is the greatest challenge for constructors. How to transfer the maximum amount of water vapor to the outside and using the same elements to stop the air circulation in an artificially or naturally insulated layer of thermal insulation? At the moment there is no optimal solution.
A critical element of the entire
layout of clothing or equipment
The most critical element of the entire arrangement of clothing or equipment is the outermost layer.
In the case of winter conditions, we come to the issue of condensation, which usually occurs on the inside of the outermost layer or single fabric. In the event of very unfavorable weather conditions (maintaining negative temperatures), a layer of ice may form under the membrane jacket or on the inside of the tent's flysheet. The latter phenomenon is particularly troublesome in the case of single-skin tents. The chance of ice appearing here is directly proportional to the extent to which the coating will reduce breathability. However, the problem of water vapor condensation does not only apply strictly to external coatings. It also occurs in other items of equipment, such as sleeping bags. Therefore, a sleeping bag with a cover without a membrane or with an uncoated fabric will be a better choice for the tent. A sleeping bag made of coated fabric or with a membrane will work best only for short-term use, for example in snow caves. Prolonged use will cause a significant increase in the amount of moisture in the internal structure of thermal insulation. With each subsequent overnight stay, we will need more energy expenditure to ensure the level of comfort as from a structure devoid of such a solution. This is confirmed by both laboratory tests and long-term field tests.
Thermal Hybrids
Hybrids, both as sets and stand-alone constructions, are designed to limit the potentially negative effects of using uniform layers of clothing.
Natural down ensures the highest insulating parameters, while the synthetic layer minimizes the risk of down getting wet and thus reducing its insulating parameters. In order to prevent water vapor condensation at low temperatures, at a very unfavorable point, fabrics are used in both products that only minimally impair their natural "breathability".
In such a system, if water vapor condenses, it will take place in an alternative to down insulation. In addition, thanks to the creation of air chambers between the individual layers of insulation, this construction ensures higher thermal performance. All this is achieved without any interference in the most perfect insulating material, which is natural down.
