All about waterproof membranes

Water- and windproof clothing that breathes well at the same time. It exists, but how can a jacket be waterproof and still breathe? In this slightly more technical blog, we will look at membranes in clothing and how exactly they work.

Table of contents

• Some key terms explained
• The building blocks of a membrane
• The number of layers
• The role of DWR
• How do you know which membrane is "good"?

Some key terms explained

To understand exactly how a membrane works, we will first need to discuss some common terms. You may well have come across these many times before, but you may not know their exact meaning. In addition, the terms are also used interchangeably by some parties. To avoid misunderstandings, we will therefore briefly go over them first.

First, we briefly discuss the terms waterproof, water-resistant and water-repellent. Water-resistant clothing provides protection against a small amount of precipitation. However, it is not able to protect you from prolonged rain or a heavy downpour. Waterproof clothing, however, is capable of protecting you from heavy precipitation for long periods of time. By water-repellent, we mean the effect that water does not absorb into your clothing during a shower, but instead creates droplets on the surface that then slide off. So the water is actually repelled. You can read more about these terms in our blog on the differences between water-repellent, water-resistant and waterproof.

The water-repellent effect just described is often caused by DWR impregnation. Especially in clothing. DWR stands for "Durable Water Repellent". In our blog on Durable Water Repellent, we explain in detail exactly how such impregnation works. For this blog, it is first important to know that a DWR impregnation will not repel all water during prolonged precipitation. It is then up to any membrane to prevent the unrepelled water from penetrating the fabric. How well such a membrane does this will therefore determine whether the garment is ultimately waterproof or water-resistant.

Finally, breathability. By this, we refer to the ability of the material used to transfer heat and perspiration away from your body to the outside. Material with good breathability prevents you from getting wet from the inside. You can read more about this in our blog on the breathability.

The building blocks of a membrane

So, as mentioned, the membrane ultimately allows a garment to be waterproof. But how exactly does it do that? To find out, we need to find out how a membrane is constructed. Almost all membranes for clothing are made of ePTFE or non-porous materials such as polyester and polyurethane.

Microporous

Expanded polytetrafluoroethylene (ePTFE) is a material developed by Bob Gore and used to make the first Gore-Tex fabrics in 1978. Bob Gore discovered that when PTFE is "stretched", it creates a kind of waterproof web with millions of microscopic pores. These pores are 20,000 times smaller than a water molecule, but 700 times larger than a water vapour molecule. This means that liquid water cannot pass through the membrane, but gaseous water vapour can. Such material is therefore waterproof and breathable at the same time.

A disadvantage of ePTFE membranes is that they contain harmful PFCs. Therefore, more environmentally friendly alternatives are constantly being sought. Meanwhile, Gore-Tex has launched the ePE membrane. This is not made of expanded polytetrafluoroethylene, but of expanded polyethylene. This type of membrane is PFC-free.

Nonporous

Polyester and polyurethane (PU) contain no holes or pores (which therefore cannot get clogged) and are therefore called nonporous. At the same time, the materials are also hydrophilic, which simply means that there are small molecules with a strong affinity for water in the materials that want to transport moisture outside. These hydrophilic molecules move faster through the material at higher temperatures, regardless of whether that is caused by the ambient temperature or your body temperature. In other words, as humidity and heat increase on the inside of the jacket, the difference between the inside and outside temperature causes the molecules to transport more moisture outside. This also means that this type of membrane breathes best when you are warm and the outside temperature is on the low side. Membranes made of polyester or polyurethane are 100% recyclable.

The number of layers

The membrane is usually protected on both sides. On the top side (the side in contact with the outside world), the membrane is protected by a fabric we call the upper fabric. On the inside (the side in contact with your skin or undergarments), protection is provided by a type of lining. We find this construction (upper fabric - membrane - lining) on the outdoor market in three different variants.

2-layer

A 2-layer construction consists of the membrane bonded to the upper fabric. This together is called a laminate. This laminate is protected by a liner that prevents direct contact of the membrane with the skin. This is a so-called suspended lining, meaning that it is not bound to the laminate. The lining protects the membrane on the inside and also provides higher wearing comfort. On the other hand, the lining also adds weight.

A 2-layer construction is found mainly in the lower-cost segment of rainwear and in waterproof clothing with an insulating padding. In the latter case, the filling material is located between the laminate and the suspended lining.

2.5-layer

A 2.5-layer construction is very similar. The difference is in the lining. This is because it is replaced in the 2.5-layer version with a wafer-thin "sprayed-on" layer (the 0.5 in 2.5) directly on the inside of the membrane. This layer is a lot lighter and more compact than the suspended lining of the 2-layer construction. Also, the breathability of the 2.5-layer version tends to be better. At the same time, the inside does feel less comfortable on the skin.

Because of its very light weight and compact properties, you will find this 2.5-layer construction especially in waterproof jackets that you actually only wear when it actually rains. Once it has stopped raining, you can easily store the jacket in your backpack without taking up too much space.

3-layer

Also in a 3-layer construction, the membrane is bonded to the upper fabric. This laminate is then bonded with the membrane side to a third protective layer. This layer is also called a backer and its main purpose is to protect the laminate without greatly reducing breathability. Wearing comfort is secondary to this.

The 3-layer construction usually offers the very best protection against wind and water, generally breathes better than a 2-layer construction and lasts longer than the 2.5-layer variant. It is also normally the sturdiest of the three constructions. We therefore find this construction most often in clothing for activities where the different layers can take a bit more beating. Examples include alpine tours, trekking and off-piste skiing.

Alternatives

On the "upper fabric - membrane - protective layer" construction, there are also alternatives. For example, Gore-Tex's ShakeDry membrane has no protective upper fabric. The membrane is thus the top layer. For certain activities, this may not be an objection. Think, for example, of running, trail running or cycling (all without a backpack).

The role of DWR

The vast majority - but not all - of clothing with membranes feature DWR impregnation (Gore-Tex's ShakeDry is an example of an exception). Often in the form of a coating on the upper fabric. This coating has an important role in the functioning of the membrane. That role becomes clear once the DWR coating starts to wear off. The garment then becomes less water-repellent and will therefore absorb more water. Eventually, the laminate becomes flooded with water. The garment will then still retain its waterproof properties (thanks to the membrane), but its breathability will be largely lost. As a result, the inside of your garment can still get wet (in the form of perspiration)..

It is quite common for a DWR impregnation to wear out over time and with regular use. This is even more true of modern PFC-free DWR impregnations. However, there is fairly little you can do about this. Fortunately, it is possible to restore the DWR of your clothing using special care products. You can find more information on this in our blog on maintaining technical garments.

How do you know which membrane is "good"?

The term good is in inverted commas here, because there is no such thing as the best membrane or the best number of layers. There are many different outdoor activities and therefore at least as many different "best" membrane products. What is very important to you? Are you mainly looking for protection against precipitation? How well should the membrane be able to breathe? And should the fabric also be sturdy and hard-wearing? And do you really need the best of the best or will a decent product for your activity also suffice?

If you have answers to all these questions, by the way, you are not there yet. Because how do you know how well a membrane protects you from precipitation. Or how well it breathes? Fortunately, there are some indicators that can give you more information about this, but unfortunately even these do not always offer 100% certainty. We list them here.

Water column

The water column of a fabric indicates how much pressure is needed for water to penetrate a fabric. The higher the water column (shown in millimetres), the more pressure is needed and therefore the better the protection against precipitation. The water column is measured using a test. You can read exactly what such a test looks like in our blog on the water column of a fabric. For now, it is good to know that there are different types of tests and measurement methods. It is certainly possible for a substance to get a better result in one test than in another. So that's why you shouldn't be blinded by a product's stated water column.

The MVTR & RET

If breathability is important to you (and quite often it will be if you are looking for products for outdoor activities), your best bet is to look at the MVTR or RET rating that you will regularly find on items with a membrane. These tell you something about a fabric's breathability. To find out exactly how to interpret these values, read our blog on MVTR and RET measurement methods. For this blog, it is important to know that the higher the MVTR value is, the better the fabric breathes. With the RET value, this is exactly the other way around. So the lower the value, the better the breathability.

Firmness of the upper fabric

Depending on your activity, the degree of strength or resistance to abrasion of the protective upper fabric is also important. You can derive this from the denier of the upper fabric. The higher this number, the sturdier and more abrasion-resistant (but also heavier) the upper fabric.

Producer reputation

Another indication of the quality of a membrane is its manufacturer. Gore-Tex is the best-known manufacturer of membranes and enjoys an excellent reputation in the outdoor world. Many outdoor enthusiasts swear by Gore-Tex. To what extent this is only due to the quality of the membranes and not also a little bit due to the company's active marketing policy is hard to say. Other well-known membrane manufacturers include Pertex, Sympatex or Toray, known for Dermizax. Finally, there are also clothing manufacturers who make their own membranes. Often for the more budget-friendly part of their range. By the way, this does not mean that these membranes are necessarily of lower quality.

Online reviews

Finally, it can also be well worthwhile to look for online reviews. Although the Internet is full of sponsored (and therefore not always reliable) product reviews, this is still an excellent source of information. There are also all kinds of (international) forums, where you can go for more disinterested product experiences. It just sometimes takes a good search.

Hopefully, with this blog we have been able to explain to you exactly how membranes work and the differences between them. And if all goes well, you now know what to look for when assessing the quality of a membrane. If you still have questions after reading this blog, do not hesitate to contact our customer service team. We will be happy to help you with all your questions.