What is a pillar of jacket

Breathable - what does that mean? Everything about RET and MVTR

Ski clothing, rain jackets, fleece shirts and softshell trousers: outdoor and mountain sports clothing, along with other functionality, is mostly breathable. But what does that actually mean and how does it work with the breathability of Gore-Tex, polyester fleece and softshell materials?

What does breathable or breathability mean?

The term breathability is a colloquial term for water vapor permeability. Breathable is understood to mean the ability or possibility that water vapor can escape from the inside of a textile to the outside. Especially in (outdoor) sport, breathable clothing ensures a more comfortable, drier wearing climate and helps to counteract excessive sweating and overheating.

Membrane, softshell & fleece: what is breathability based on?

Regardless of whether it is a functional shirt or a rain jacket - the breathability of textiles is basically based on trivial physics and chemistry. An example: a jacket keeps body heat on the wearer. With increasing activity, body temperature rises - you start to sweat. This increases the temperature and the concentration of the water vapor - and thus the pressure - inside the jacket. Due to the difference in temperature and humidity between the inside and outside, the water vapor migrates through the textile from the warm inside to the cooler and drier outside. This is called diffusion and the higher the gradient, the better it works.

Contrary to what the term “breathable” might suggest, jackets or textiles of this type themselves do little to wick away moisture. However, they offer the possibility that body moisture can escape more or less well from the inside. How exactly - whether by capillary force or osmosis - and how quickly the water vapor molecules penetrate the textile depends on the material, its composition, structure and structure. Our material information provides more details.

How is breathability measured?

For measuring the breathability of functional textiles such as softshell and waterproof LaminatesThere are mainly two test methods used: MVTR and RET.

  • The Moisture Vapor Transmission Rate or the MVTR test measures the amount of liquid that has evaporated over a certain period of time. The MVTR test is not clearly standardized, so the results can be different if the test and laboratory conditions (temperature and humidity) change. The air permeability of the fabric is also not taken into account. In addition, it is generally not possible for the end customer to understand whether the test was carried out on the bare membrane, on the laminate or on the finished item of clothing.
  • The Resistance of Evaporation of a Textile (RET) indicates the water vapor resistance. The force that the water vapor needs to get through the tested textile is measured. For the test, the finished garment is placed over a porous sintered metal plate that is electrically heated to 35 degrees Celsius and through the pores of which water vapor escapes. This simulates the skin's sweating process. The test carried out under standardized conditions in the climatic chamber is considered to be relatively independent of fluctuations in temperature and humidity. The test method, the so-called Hohenstein test, was developed in the 1970s by the Hohenstein Institute and standardized by the ISO standard 11092. With ASTM F1868 and DIN EN 31092 there are further test standards for the RET. The Stiftung Warentest last used the RET in 2016 to evaluate the breathability of rainwear.

How is breathability indicated?

Depending on the test method used, the breathability is usually given as a RET or MVTR value. While the RET is converted into an abstract value on the RET scale, the MVTR value indicates the amount of evaporated liquid per cubic meter in 24 hours (example: 15,000g / m2 / 24h). Sometimes you can also find simplified MVTR information such as "Breathability: 10,000".

What are good values?

MVTRRET to Hohenstein
not breathable > 20
breathable from 3,000g / m² / 24h Until 20
very breathable10,000g / m² / 24h6 – 13
extremely breathable 15,000 to 40,000g / m² / 24h < 6

The EMPA (Federal Materials Testing and Research Institute) sets the RET benchmark for extremely breathable and very breathable textiles with values ​​<4 or 4 to 8 somewhat more strictly than the Hohenstein Institute. A RET value above nine is considered “moderately breathable” by the Swiss, and above 21 the water vapor permeability is “low”.

  • Note: Both MVTR and RET are only to be understood as guidelines when selecting a product. In terms of air pressure, temperature and humidity, the actual conditions of everyday outdoor life usually have little to do with those in the test laboratories. There is also wind and movement. Deviations from theory to practice are therefore more the rule than the exception.

Water column and breathability: how are they related?

At first glance, the matter is quite simple: the more waterproof, the less breathable a textile material is. The height of the water column limits the possibilities of water vapor transport - often, but not always.

If you take a closer look, then this relationship - especially with breathable rainwear - cannot be determined across the board and in the same form for all waterproof materials. Laminates specializing in rapid moisture transport, such as Gore-Tex Active or Dermizax NX, achieve top values ​​in the area of ​​breathability in the laboratory tests despite a very high water column. On the other hand, there is also total density Coatings - for example with the classic Friesennerz - which do not allow any water vapor to escape to the outside.

So it is good to know that the water column and breathability are not a standardized or fixed ratio. Depending on the manufacturer, product or textile laminate, the information on breathability can vary greatly with the same water column. With a view to wearing comfort, the information on breathability for waterproof rainwear is the more interesting measure. Both values ​​are helpful in order to assess the functionality to be expected.

Breathability and durability: is there a connection?

When it comes to rainwear, greater breathability often comes at the expense of durability. Thin and light fabrics for ultra-light rainwear such as Gore-Tex Active are made for intensive sport - not for heavy backpacks. Such jackets do not offer the same resistance as more robust laminates with stronger outer fabrics and stronger membranes. If used incorrectly, they wear out quickly.

Is windproof clothing breathable?

Yes, but air circulation is more or less restricted in windproof and windproof clothing. Here, too, the breathability decreases the “denser” the textile is. How strong also depends on the structure of the textile: Strongly wind-repellent softshells with just one very tightly woven surface are more breathable than laminates with a windproof membrane.

What hinders the breathability of functional clothing?

Does your breathable rain or ski jacket make you sweat? There can be several reasons for this.

  1. Its to warm.
    So that the removal of moisture works in principle, there is a need between the inside and the outside Temperature gradient of at least 15 degrees Celsius. Only then can the water vapor diffuse. At higher temperatures above 20 degrees or too many insulating layers of clothing, the moisture transport comes to a standstill - or completely refuses to work. Note: In the tropical rainforest, Gore-Tex and Co. protect against rain, but you still get wet - from the inside.
  2. The material is too cold.
    Sometimes it happens that sweat condenses on the inside of the textile because the material is too cool. This is a similar phenomenon to condensation on cold walls in insufficiently heated rooms. Condensing moisture is more noticeable with 2.5-layer laminates than with three-layer laminates. Here the textile lining absorbs part of the moisture on the inside.
  3. It's too exhausting.
    The diffusion of water works in the form of water vapor molecules. However, if the liquid sweat runs in streams, the membrane can no longer keep up with the removal. Condensing water on the inside of the clothing often gives (incorrectly) the impression that the laminate is no longer tight. Tip: Additional ventilation options such as pit zips under the arms or ventilation slots on the thighs facilitate - to a certain extent - the removal of moisture.
  4. The impregnation is bad.
    If the factory DWR treatment wears off due to wear and tear or repeated washing, the rain no longer runs off the outside. If a closed film of water forms on the outside of the material, one speaks of the so-called "wetting out". The layer of water blocks the evacuation of sweat, and breathability finally comes to a standstill. Tip: For this reason, the DWR treatment should be checked regularly and reactivated or renewed if necessary.Manual:Impregnate the rain jacket - that's how it works!
  5. The pores are clogged.
    Insufficient care can also hinder breathability. Regular washing is especially important for microporous membranes for optimal functionality, as the fine pores can become clogged with sweat residues and dirt. Tip: Microporous membranes should only be cleaned with liquid detergent, as washing powder residues can also be deposited in the pores. Manual:Wash and impregnate Gore-Tex clothing properly!
  6. The way is blocked.
    It should also be mentioned briefly at this point that functional clothing can only "breathe" when the steam really has free rein. That means: the backpack and too many insulating layers of clothing can also hinder the transport of water vapor. In the case of breathable rainwear in particular, the layers of clothing underneath should also support the removal of moisture. Reading tip: What is the onion principle?

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