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Breathability in a rain jacket

Here’s what you should consider

© Columbia

Would you rather avoid taking a shower in the rain while bathing in your own sweat when you are out and about? Then breathability is especially important in your new rain jacket. Find out here what breathability really means and how to find the best jacket for your needs.

When you are looking through the range of rain jackets, comfort and weatherproofing play a crucial role – after all, you don’t just want to get from A to B, you want to enjoy the outdoors to the fullest. Especially when it comes to a rain jacket, breathability plays a crucial role in whether your skin can breathe – and whether you can, too.

What does breathable mean?

The breathability of a fabric tells us how open it is to diffusion, or to put it more simply: breathability is about how well a fabric can transport water vapour away from the body to the outside.

Breathability is affected by various factors:
  • How tightly is the fabric woven?
  • What materials are used?
  • Is there any additional impregnation?
  • Is the fabric rainproof or windproof?

The more breathable a fabric is, the better and drier it feels. If a rain jacket is particularly breathable, you will sweat much less quickly and heavily in it than in other fabrics. This is because the evaporating moisture can escape to the outside without much resistance in a breathable rain jacket, which means the skin is cooled immediately and less sweat is produced.

If, on the other hand, the rain jacket does not let any water vapour through to the outside – if it is not breathable – moisture and temperature will continue to build up inside the jacket. Your body tries to regulate the resulting imbalance by sweating more. The result: The inside of the fabric gradually becomes soaked and your rain jacket ends up just as wet on the inside as it is on the outside.

© Columbia

How is breathability measured in outdoor textiles?

There are two basic methods for measuring the breathability of a rain jacket or other outdoor clothing: measuring the permeability with the MVTR test and measuring the water vapour transmission resistance using the RET method.

The MVTR method

The value for the MVTR (Moisture Vapour Transmission Rate) indicates how much water vapour penetrates through a fabric surface of one square metre within 24 hours – it is therefore given as g/m²/24h. The higher this number, the more permeable the fabric is and the drier your body climate will remain during outdoor activities. This means: The higher the MVTR value, the better the breathability of the rain jacket.

High-end outdoor clothing designs reach peak values of up to 40,000 g/m²/24h in the MVTR measurement. In general, however, a garment is considered very breathable above 10,000 g/m²/24h. A disadvantage of the MVTR test is that there are no clearly defined test conditions. The breathability of one and the same rain jacket can therefore vary significantly even with slightly different laboratory conditions.

The RET method

The RET (Resistance to Evaporation of a Textile) value measures the resistance of a fabric. With this measuring method, you are looking for as low a value as possible, because the less resistance there is to the water vapour, the easier it is for the humid air to diffuse through.

RET values are given in m²/Pa/W, although often only the number is given. There are two institutions that measure RET values: the Swiss Federal Laboratories for Materials Science and Technology (EMPA) and the Hohenstein Institute. Both use the same method, but classify the results differently.

Table: Breathability in outdoor textiles - the MVTR and RET method
BreathabilityMVTRRET value HohensteinRET value EMPA
extremely breathable15,000–40,000 g/m²/24h<6 m²/Pa/W<4 m²/Pa/W
very breathable10,000–15,000 g/m²/24h6–13 m²/Pa/W4–8 m²/Pa/W
breathable3,000–10,000 g/m²/24h13–20 m²/Pa/W9–20 m²/Pa/W
barely / not breathable0–3,000 g/m²/24h>20 m²/Pa/W>21 m²/Pa/W

When buying a rain jacket or trousers, you should still keep the overall package in mind. Even though breathability is an important feature, the measured values in the laboratory often differ considerably from outdoor use. This can happen, for example, with a change in humidity, temperature or air pressure, your level of movement or the load from luggage or the wind.

Breathable even with at high water column

Good breathability of your rain jacket is always important – but especially if it also has a high water column. The water column is a guideline for the pressure to which your rain jacket can be exposed without rainwater or snow penetrating through to the inside of the fabric. The higher the water column, the less permeable the material is to moisture from outside.

A waterproof rain jacket protects you less well than a water-repellent jacket. But you will stay dry the longest with a waterproof rain jacket with a high water column.

Generally speaking: a high water column makes good breathability of the rain jacket all the more important, because arriving at your destination drenched in sweat is at least as unpleasant as getting soaked by the rain.

Breathable waterproof jackets

Waterproof on the outside, permeable on the inside – how does that work?

If you want maximum comfort for your body during outdoor sports, your rain jacket should simultaneously protect you from moisture from the outside and take moisture away from the inside. But how is that actually supposed to work – aren’t breathability and weather resistance mutually exclusive?

The magic term here is the physical state: a breathable membrane does not let sweat through as a whole drop of liquid, but only in the form of the water vapour that is produced. The sweat that forms on your skin initially evaporates with a cooling effect into tiny water droplets that float in the air. These small particles are tiny enough to pass through the fine pores of the fabric.

© Columbia

Breathable clothing does not actively conduct water vapour to the outside, however, but merely allows it to escape. Ventilation happens automatically through nature’s pressure equalisation. Excess heat and water vapour are then pushed through the various fabric layers of the rain jacket as if by magic. The result: your skin stays pleasantly dry and cool even when you are moving – perfect for sporting activities.

Membranes & laminates: the technology behind the dry skin feeling

Good breathability of a rain jacket is made possible above all by its multi-layer design. You will find 2-layer, 2.5-layer and 3-layer products on the market. The basic structure of a multi-layer rain jacket is as follows:

  • water-repellent fabric side outside
  • protective membrane/coating in the middle
  • soft fabric lining on the inside

Whether a jacket is 2-layer, 2.5-layer or 3-layer depends mainly on how the individual layers of fabric are held together: 2-layer models have a loose inner lining, while the outer fabric and membrane are bonded together. By contrast, with a 3-layer design, all three layers are bonded, which usually makes the rain jacket particularly robust and light at the same time. A 2.5-layer jacket, on the other hand, uses only a thin protective layer instead of an inner lining.

© Columbia

The difference between laminate and coating

Laminates or coatings in particular are crucial for the breathability of a rain jacket – because the robust middle protective layer stops wind and rain from penetrating, but must also allow moisture to escape from inside the jacket to ensure a comfortable body climate.

The middle layer between the inside and outside of the jacket can therefore be designed in two different ways: the jacket core can be made of a laminated membrane or a coating. High-quality membranes are laminated – i.e. glued – over the entire surface of the inside of the outer material using a special adhesive. This makes them particularly robust. Gore-Tex and Dermizax, in particular, use excellent technologies here.

Whether laminate or coating: the quality can vary considerably from rain jacket to rain jacket. So always check the water column and MVTR or RET value.

A breathable coating is a cheaper alternative to the more expensive membrane. Depending on the quality, it is sprayed onto the inside of the outer fabric in one or more layers. A coating is usually a more sensitive and less durable alternative to laminate. However, if you are looking for a good value casual rain jacket for emergencies, you can’t go wrong with a good coating.

© Columbia

Breathable and robust?

Unfortunately, breathability often comes at the expense of the robustness of a jacket. The more open-pored, thinner and therefore more breathable a fabric is, the more suitable it is for intensive and sweaty sports. However, it also wears out more easily if you are carrying heavy bags on your shoulders. So if ruggedness is just as important to you as good breathability, look for high-quality, three-layer laminates and strong, sturdy outer fabrics made of nylon or polyamide.

What can affect breathability

The same conditions do not prevail outdoors as in the laboratory. Even if your rain jacket performs well in terms of RET or MVTR, it may reach its limits in some situations.

This applies, for example, to:

  • warm, humid weather
  • high air pressure
  • high humidity
  • heavy perspiration
  • dirty pores

For breathability to work ideally, it must be at least 15°C colder on the outside of the jacket than on the inside. In summer, the breathability of a jacket therefore only helps to a limited extent, if at all. If you are sweating due to heavy exertion, the ventilation also struggles to keep up. In order to maintain the breathability of your jacket, you should also wash it regularly.

Breathability in all layers

Over the years, outdoor clothing has improved significantly in terms of comfort, weather resistance and robustness. Especially when it comes to breathability, you should make sure that all the other layers of your clothing are permeable as well: the most breathable rain jacket is ineffective if the moisture does not get through the base layer in the first place. However, overlaying layers such as a backpack can also limit the breathability of your rain jacket by adding pressure in certain areas.

The checklist: everything you need to know about the breathability of your rain jacket at a glance

  • Breathability describes the water vapour permeability of textiles
  • The MVTR or RET value indicates how breathable a product is
  • High-quality laminates or coatings are important when it comes to making a purchase
  • Tailor the jacket to your activities, the rain level and any bags you will be carrying
  • The best breathability is achieved in dry, cool weather
  • Optimise breathability even in the underlying layers of clothing

Conclusion: Breathability is crucial in a rain jacket

When it comes to breathability, you should not compromise on your rain jacket. The permeability of the structure to water vapour keeps your body cool and dry, even during strenuous outdoor activities.

Thanks to sophisticated membrane technologies and coatings, your jacket will become an indispensable companion. This applies if you value lightness and flexibility on the move, if you are climbing the Alps with heavy bags on your shoulders, or if you are only in your element in rain or stormy weather. If you adapt your rain jacket to your personal requirements, you will arrive at your destination dry and comfortable.