An introduction to breathability

22. December 2017


Breathability is a very important aspect of functional clothing

Breathability is a very important aspect of functional clothing

The word breathability is used constantly in the outdoor industry.

But, what does breathability really mean? Is your shirt really breathing? If so, what’s it breathing in? The outside air or the vapour coming from our bodies? And why is breathability so important?

Well, we’ll tell you! We’ve put together the most important information on the topic of breathability

breath·a·bil·i·ty [ˌbriːðəˈbɪlɪtɪ] : ability to let air pass through; Example: the fabric is breathable.
Part of speech: noun
Usage: Advertising
Frequency: 2 of 5

You won’t find much more about the word in the dictionary, which is the first thing I consult when I don’t know the meaning of a word. In fact, that’s exactly what I did when I saw the wonderful topic “What’s does breathability mean?” on my to-do list. But that’s not to say that I didn’t know what it meant. How could I not? I mean, it’s literally everywhere. There’s not one outdoor garment that can get along without having – at the very least – breathable properties anymore.

When asked what breathability actual refers to, most would say something to the effect of: “Isn’t that when your shirt doesn’t stick to your body even after sweating so much?” Yep, that’s basically it! Nevertheless, breathability is not really the best word to describe this phenomenon. I mean, since when can dead matter breathe anyway? Ok, let’s get to it: what’s the deal with breathability?

If you exercise, you’re going to sweat.

Breathability has to do with what happens to all the sweat when you perspire

Breathability has to do with what happens to all the sweat when you perspire

A no-brainer, right? An active person produces energy! But, not all this energy is put to good use. Approximately 20% of this energy is converted into mechanical energy, with the rest being released in the form of heat. Obviously, this isn’t particularly efficient, so the body is forced to come up with a way to regulate its temperature.

The solution is 2 to 3 million sweat glands distributed all over our bodies. The majority of them are found on our palms, the soles of our feet, in the armpits, the back of the neck and forehead. Under normal physical activity conditions, the body will produce 200-700 ml of sweat each day! However, during very strenuous exercise or in hot temperatures, we can produce up to 1.5 litres of this salty discharge per hour!

So, breathability has to do with what happens to all the sweat when you perspire. If the sweat were to just stay on your skin, it could get pretty uncomfortable: As we all know, sweat promotes the build-up of heat between our bodies and the garment we’re wearing, or it can cause a very unpleasant cooling effect. You know that feeling, right? That clammy feeling of damp clothing against your skin? Absolutely dreadful, isn’t it!

When you’re exercising, playing football or engaged in any other physical activity, it is important for your clothing to have the ability to allow moisture vapour to be transmitted through the fabric and away from your body. So, when we talk about the breathability of a garment, we’re actually referring to its water vapour permeability. Of course, breathability can be measured! This is done by calculating how many grams (g) of water vapour can pass through a square metre (m2) of fabric in a 24 hour period. 5,000 g of breathability means that 5,000 grams of water vapour can pass through a square metre of fabric.

Breathability, water vapour permeability or moisture management?

Breathability is about water vapour permeability

Breathability is about water vapour permeability

To make things even more confusing, I think I’ll just go ahead and mention yet another term: moisture management or moisture wicking. When it comes to water vapour permeability, we have to differentiate between two types of material:

  1. Materials that are waterproof and are still able to allow sweat to pass through to the outside
  2. Non-weatherproof materials that allow for active moisture transfer

Textiles belonging to the second category are usually referred to as having the ability to provide moisture management. The idea behind this is that individual fabrics actively draw moisture away from the body to the outside. But, before we get into that, let’s talk about the first category!

Membrane: open or closed?

Hardshell jackets come with a technical membrane. The point of this membrane is to reliably keep wind and precipitation out whilst simultaneously providing a high level of breathability. This is something that can be achieved with the help of two different membranes: microporous membranes or closed membranes.

As the name already suggests, microporous membranes are porous, meaning they have microscopic pores. These are just big enough for water vapour to pass through to the outside, but too small for liquid water to get in, which makes the fabric absolutely waterproof. Membranes are usually made of polytetrafluorethylene and have a very thin, protective polyurethane film over it. The most well-known are Gore-Tex membranes and those by Gore-Tex’s rival eVent.

A closed membrane is a membrane that has no pores. So, what happens to the water vapour molecules? Well, moisture builds up on the inside of the jacket until the membrane swells up and the water vapour molecules can be transported to the outside. Even though these membranes are considered to be significantly more robust, it takes a while before they actually do what they’re supposed to. As for the fabric, manufacturers generally used polyester. A perfect example is the environmentally-friendly Sympatex membrane.

Cotton, Fleece, Merino and Co.

Hardshell jackets make up the outermost layer of clothing, so in order for the sweat to make it all the way to the jacket’s membrane in the first place, your base and mid layer have to pull their own weight ! It’s not so much a matter of how much moisture the fabric absorbs as it is a matter of how quickly the fabric repels it. Cotton, for example, absorbs sweat very quickly and doesn’t repel it at all, thereby preventing moisture transfer.

Synthetic fibres, such as polyester, polacrylic, polypropylene or polyamide work much better than cotton when it comes to moisture transfer. For example, on a day with a temperature of 20°C (68°F) and 65% humidity, polyester would only absorb 7% of its own weight in moisture. Plus, it would dry very quickly as well.

Another very popular fabric is merino wool, a natural fibre, which is not only soft and comfortable to wear but also has excellent properties: it absorbs moisture and draws it away from your skin and dries very quickly as well. Plus, it is odour resistant, so you’ll always feel comfortable.

The bottom line

So, what have we learnt? Breathability doesn’t refer to air after all, but to water! More specifically, it refers to moisture and how to best get rid of that moisture. There are so many different approaches to breathability in the wonderful world of functional textiles that it can be hard to keep track of them all. Some have been successful, whilst others are only beginning to make their mark. Unfortunately, there is no universal recipe for excellent breathability, so just head outdoors and see what works for you!

If you have any questions, feel free to ask our experts in customer service. They are available during the week from 9 a.m. till 4 p.m. and can be reached by phone at 03 33 33 67058 or via e-mail.

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