This article is aimed at allowing you to enter the world of waterproof breathable fabrics and clothing and get familiar with their properties and applications as well as the trends on the WBFs market.
In bad weather, your outerwear must be wind- and waterproof because it is expected to provide protection against wind and precipitation. A waterproof material is expected to fully protect from rain, snow, and wind and entirely prevent the penetration and absorption of liquid water. Usually, waterproof textiles act as a barrier between your body and the humidity in the environment. Indeed, waterproof fabrics may give you excellent protection from the elements, however, they are not able to transport the perspiration through the clothing to the outside causing a person to get wet from inside the clothing. One possible solution to this problem is given by the so-called waterproof breathable fabrics (WBFs). The technology for manufacturing waterproof breathable textiles has been constantly developing and improving since the introduction of Gore-Tex some 40 years ago. It is also quite diverse with plenty of new fabrics introduced through a steady blend of innovation and evolution. Garments made of waterproof breathable textiles are used by sports and outdoor enthusiasts and professionals in any conditions. A waterproof and breathable fabric combines two distinct functions – waterproofness and breathability. It should basically provide protection from the rain, snow, wind, and cold but also maintain comfort just below the fabric layer allowing internal water vapor to escape.
Waterproof breathable fabrics – types and features
Types of waterproof breathable fabrics
The classification is based on two criteria:
- The structure of the waterproof breathable layer.
- The technique used for developing WBF.
According to their structure, WBFs are basically: tightly woven made of long fiber cotton fabric, microporous (laminated or coated) with very small gaps throughout allowing water vapor to escape to the outside but now allowing water to permeate into the fabric from the outside, and finally the third kind is composed of nonporous structure and has been developed as hydrophilic films in which water vapor is absorbed on one side of the film and re-evaporates from the other side whilst preventing liquid water penetration. Any other types are just various combinations of two or more of these.
The main principle behind microporous membranes and coatings is the following: water drops cannot penetrate because the pores are smaller than a raindrop, while perspiration evaporates through because the pores are larger than vapor molecules. The diameter of a water vapor molecule is 40×10⁻⁹mm and the diameter of various drop types is much larger as you can see in Table 1.
Microporous membranes and coatings function well when the size of the pores on the outer surface of the fabric is no bigger than 0.0002-0.0003mm which is equivalent to 2-3μm. At the same time, the average pore size in microporous membranes is between 0.0001 and 0.005mm (1-50μm). Generally, water vapor transmission depends on the size and thickness of pores as the decrease in pore size and thickness increases the water vapor transmission.
Table 1: Diameters of various types of drops
Source: Waterproof and Water Repellent Textiles*, p.373
Figure 1: Major types of waterproof and breathable fabrics
(A) typical view of tightly woven fabric, (B) coated woven fabric and (C) laminated woven fabric
Source: Waterproof and Water Repellent Textiles, p.47
The woven fabric is dense with a minimum quantity of pores. Moreover, it’s treated with a durable water repellent (DWR) for added waterproofness. The reason is quite obvious – the pore structure should not allow water droplets to permeate through the fabric from the outside. Meanwhile, fiber fineness combined with inherent moisture absorption and the ability of the fiber to swell with increasing moisture content are some other important characteristics of tightly woven fabrics.
The very first type of such a structure is called Ventile. It’s made of quality long staple cotton fibers (fine Egyptian cotton) and was introduced in England during the WW2. How does it work? The main principle is simple. When the fabric is dry, it’s highly breathable since the cotton fibers retain an open breathable structure. At this time, the spacing between warp and weft is about 10μm. However, in contact with water, the cotton fibers absorb water and expand. As a result, the gaps shrink to about 3-4μm thus making the fabric practically impermeable to water except for the cases under very high water pressure. For better results, the densely woven fabric is impregnated with a DWR to make sure that the fabric will not be exposed to further penetration.
Nowadays, man-made fabrics such as polyester, polyamide, acrylic, and viscose are preferred for manufacturing tightly woven fabrics. The pores of these tight constructions are too small for water molecules to penetrate through but large enough to allow water vapor to pass through.
Materials that have a solid polymer-based film or coating (with high resistance to water penetration) are also used. Thin hydrophilic films are utilized because water vapor permeability rates through such kind of films depend on their thickness as thicker hydrophilic films are more permeable to liquids.
The transmission of moisture vapor is achieved thanks to molecular diffusion as the moisture is absorbed by the hydrophilic membrane or coating, diffused through the film, and released on the other side. The process is illustrated in the figure below. Sympatex is among the representatives of this type of WBF.
Figure 2: The mechanism of moisture transmission at hydrophilic structures
Source: Waterproof and Water Repellent Textiles, p.55
Membranes are thin films made from polymers. There are basically two types of membranes – microporous membranes (they’re hydrophobic) and hydrophilic membranes.
The most widely used polymers for microporous fabrics are expanded PTFE (ePTFE) and polyurethanes (PU). Microporous films have about 1.2-1.4 billion tiny holes per square centimeter. These pores are much smaller than the smallest raindrops and they usually range between 0.1 and 10μm (1mm=1000μm). At the same time, they’re larger than water vapor molecules so that they can pass through the pores of the membrane. The process is illustrated in the figure below.
The first commercial microporous layer in textiles was introduced by W.L. Gore in the 70s and consisted of a microporous structure that was about 70% air. This membrane has around 1.4 billion pores per square centimeter, with each pore 20,000 times smaller than a drop of water, but 700 times larger than a vapor molecule. The membrane is laminated to a conventional fabric to provide enough mechanical strength (the film itself is mechanically weak).
Figure 3: Working principles of microporous structure in water vapor transfer
Source: Waterproof and Water Repellent Textiles, p.49
Interestingly, breathability depends very much on atmospheric conditions. Garments using waterproof breathable membranes are resistant to wind and precipitation but in certain conditions (for instance after exposure to prolonged severe rainy conditions) breathability can be severely restricted even ceased. Fabric breathability also decreases in wet and windy weather as well as in wet and warm conditions. It turns out that wind and rain have opposite effects on the water vapor transfer rate of fabric as wind increases it while rain decreases it.
Nowadays, Japan is a pioneer in the production of new microporous coatings and laminates. In the last 10 years, Japanese companies have developed a number of new microporous coatings and laminates. Among the main reasons for this are the vast home market and export capacity for synthetic-based wear. Europe is also a big player and a major market for membrane-based waterproof breathable textiles thanks to the high popularity of outdoor recreation and nature tourism.
Bi-component structures are a combination of microporous and hydrophilic membranes and coatings. Hydrophilic membranes are coated with a thin hydrophilic layer to increase waterproofness and to seal the surface pores, thus reducing the possibility of contamination of the microporous layer by dust particles, detergents, pesticides, etc. A hydrophilic finish (often chemically modified PU or polyester by incorporating poly(ethylene oxide) on a microporous structure is used to upgrade the water-resistance of microporous coatings. This ensures enhanced waterproofing capacity while allowing water vapor molecules to pass through at the same time.
Biomimetic and smart waterproof breathable textiles
Inspired by nature, biomimetic fabrics are designed to mimic the structure and function of naturally occurring materials and processes. The advent of many discoveries and inventions have stemmed from observing and imitating natural processes and mechanisms. The producers of biomimetic fabrics often draw inspiration from biology and try to find practical applications and/or develop outdoor products in the field of high-performance and functional textiles.
A breathable fabric with temperature-dependent response; adaptive insulation mimicking penguins in extreme cold conditions; water-repellent fabrics based on superhydrophobicity or a lotus leaf reaction towards water (it beads up and rolls off, cleaning the leaf’s surface in the process) are just a small part of all biomimetic projects related to high-performance and functional textiles.
Main properties of waterproof and breathable textiles
The main principle of how waterproof breathable textiles function (regardless of the fabric construction) depends on the relative humidity levels: if it’s more humid inside the jacket than outside, moisture will want to move outward to establish equilibrium and the opposite – if it’s more humid in the ambient environment than inside the outerwear, moisture will want to move inward. Therefore, the exterior face fabric of the jacket is critical for the passage of moisture meaning that the DWR applied must keep the face fabric drier than the inner side to allow the escape of interior moisture.
Durable water repellent
Various finishes can be applied to the outer layer of a fabric providing effective repellency against water, oil, and dry dirt. Durable water repellent is a coating capable of repelling water. It is used to impart hydrophobicity to a fabric or simply to make it water-resistant without adversely affecting breathability.
Why do waterproof breathable fabrics need DWR treatment?
DWR treatment is used on waterproof fabrics to make drops bead on the surface and easily drip off instead of spreading on the fabric and wetting it. This prevents rain and snow from saturating the garment’s exterior maintaining fabric’s breathability.
The most popular techniques are two. The first one is to use a DWR that decreases the pore diameters of the fabric. Another technique is to cover the surface with an extra layer of a nonporous or microporous material that can keep out even the smallest water droplets. There are various ways of applying hydrophobic finishes. It can be done by using spray, wax, and lick roller as well as by padding.
Fluorochemical finishes (fluorocarbon finishes)
Used since the 1960s, they provide effective repellency against water and oil-based substances and ensure easy cleanability (easy removal of dirt and soil). The idea of using fluorocarbon finishes is to form a chemical barrier against water penetration. Such finishes are durable and usually survive washing and dry-cleaning without a problem, however, ironing or tumble drying might be necessary after the cleaning. Keep in mind that before the application of such DWR, the fabric should be clean (wash away dirt and oils) and free from residual substances such as detergents and emulsifiers. Fluorochemical based chemicals are commonly used in water repellent finishes or outwear clothing because of their effectiveness and durability.
Silicone-based water repellents
Silicone compounds are used as hydrophobic coatings in the clothing industry because of their water repellency abilities. They are relatively cheap, easy to process, and can be effective. Silicone-based DWR can enhance the water repellency of fabric without interfering with its permeability. They also improve the tear and abrasion-resistance of textiles, reduce shrinkage, and make fabrics more comfortable. Silicones are often used instead of fluorocarbon water repellents because they are more environmentally favorable. However, silicone compounds aren’t as effective as fluorocarbons as they aren’t as durable as them and don’t make fabrics oil and soil-repellent.
The water repellents aren’t permanent solutions so regular maintenance and restoration of the water-repellent coating is very important and shouldn’t be neglected. Be careful and always follow the instructions to avoid adversely affecting other desirable properties of the fabric.
The most important features of waterproof breathable materials are two functions: waterproofness and breathability. The former refers to a material impervious to water, while the latter term refers to the ability of a fabric to allow water vapor to pass through it. Since total waterproofing and total breathability are mutually exclusive ideas, the concept of waterproof breathable fabrics implies some compromise between waterproofness and breathability. The precise balance depends on various factors such as the end use of the fabric, the fabric properties like moisture absorption, and the fabric construction including its density and thickness. Waterproof material for clothing can offer complete protection from the elements only if its seams, zips, joints, and pockets are waterproof as well. The number of openings through which water can penetrate should also be minimal. This guarantees that even if you’re exposed to wind and driving rain or snow, your waterproof clothing will keep you dry. Waterproofing without breathability often means protection from the outside and wetting from the inside as water vapor won’t be able to escape. As a rule, breathability or water vapor permeability ensures improved microclimate and thermal comfort.
The most popular way to measure waterproofness of fabric is by applying hydrostatic pressure measured in mm. Different manufacturers use different numbers to label a fabric “waterproof” so sometimes it can be really difficult to figure out if a material is truly waterproof or not. Now if the water column is at least 5000mm, the fabric is usually considered truly waterproof, although the minimum level can be as low as 1000mm according to some manufacturers.
Table 2: Fabric waterproof ratings
Many people are wondering what breathability of fabric means. Although this term is often associated with air permeability and ventilation, it has nothing to do with these two. Instead, it is the ability of a fabric to allow moisture vapor to pass through it. In short, breathability = water vapor permeability. The fabric must allow perspiration to be transported from the skin to the outside of the garment providing comfort to the wearer. This way, moisture build-up on the inside of the garment is avoided. It’s an important requirement for maintaining acceptable temperature and comfort at various exertion levels and conditions.
There are various methods for measuring the breathability of a WBF. One of them is through measuring moisture transmission – MVTR (moisture vapor transmission rate). The value represents the rate at which moisture passes through a square meter of the fabric in 24 hours. It is measured in g/m2 per day. Just as with the waterproofness ratings, most manufacturers apply various methodologies and tests to determine the breathability of fabric so don’t just blindly accept what you’re told by the producers about the ratings of their outdoor products. Their main goal is to promote more sales so they have a serious reason to inflate the ratings of their products.
Table3: Fabric breathability ratings
WBFs are used mostly in the clothing industry, in particular in sportswear, workwear, and leisurewear. Functionality becomes a top priority, however, it must be combined with subjective and objective features such as style, quality, comfort, weight, and price. Depending on the particular outdoor activity, the importance of one or more of the aforementioned features can vary from the most important feature to a completely irrelevant one. Colors can also play a significant role since for forestry, fishing and hunting users often prefer camouflage patterns or muted colors, while professionals such as policemen, firefighters, construction workers rely on clothes in bright colors like yellow, orange, and red. Waterproof breathable jackets, parkas, pants, hats, gloves, socks, and shoes are among the most popular products on the WBFs market. In addition, crew members of all kinds of vessels, including military and passenger ships use gear with WBFs. The primary function of the garment is in case of an emergency to delay the onset of hypothermia, thus extending the survival time and increasing the chance of escape or rescue. WBFs are indispensable to cold-weather expeditions. Especially useful for Arctic, Antarctic or high altitude expeditions, they ensure more comfort and better protection from the elements. In cold conditions, you need a waterproof insulated jacket and pants to keep you warm and dry as well as waterproof boots. They are especially useful for trails and easy snow routes and together with a pair of gaiters can help keep feet drier in wet conditions. Be warned, though, that no membrane can keep your feet dry in prolonged wet conditions so you can’t rely too much on your waterproof boots. Additionally, the membrane can easily get clogged up with dirt and sweat and on such occasions, it will stop providing adequate protection. A waterproof pack can also be very useful because it will keep your gear safe and dry. The military and law enforcement also use waterproof and breathable materials for cool-to-cold and extreme conditions because they provide excellent protection not only from precipitation but also from the wind. And, as you probably know, cold and windy weather leads to hypothermia much faster than cold and windless weather does. Workers in the offshore oil and fishing industries are among those who are regularly exposed to harsh conditions including low temperatures, wind, and rain. This determines the need to use fully seam-sealed waterproof breathable protective clothing and footwear that’s also flexible enough to allow them to work on deck and move around.
Other applications include:
- Agriculture – groundcovers for weed control, packaging for product transport, and tree shelters.
- Outdoor gear – tents, umbrellas, hats, gloves, skiwear, sleeping bag covers, fasteners, and sealings.
- Medical – bed sheets, pillow protectors, stretchers, hygiene products, orthopedic orthoses, modern wound dressings, wheelchair cushions, surgical drapes.
- Construction – used in roofs because of their lower weight, resistance to water, sound insulation capacity, UV resistance, and controlled translucence.
Table 4: Typical usage areas of waterproof breathable fabrics
Source: Waterproof and Water Repellent Textiles, p.35
It is a billion-dollar business ($1.43 billion in 2014 as membrane products account for 71%) and market research and management consulting companies like Grand View Research Inc. and Global Market Insights Inc. predict that it will expand further with between 5 and 6% on average in the next several years. There are numerous reasons for this as the main ones include: growing market for active sportswear and rising demand for waterproof breathable clothing and gear (nearly 80% of the WBFs market share belongs to the production of active sportswear), increased awareness of the need for sustainable and environmentally friendly products from the consumer, and increased demand for military and medical applications.
Currently, Europe has the biggest market share (about 30% of the market), however, Asia-Pacific is expected to have the highest growth rate thanks to the rapidly expanding market for waterproof breathable clothing and footwear in China. The major players in the waterproof and breathable textiles industry come from the US, Europe, and Asia as the industry has changed a lot during the last two decades. While the production of WBFs was concentrated almost entirely in the US, Europe, and Japan, nowadays the biggest players manufacture predominantly in Asian countries like China, Taiwan, South Korea, and Thailand. Especially in China, there is a boom in the technical clothing manufacture, which has led to a global decrease in fabric and finished garment prices due to the lower costs and rising competition.
Market leaders include companies like Toray Industries Inc. (Japan), Teijin Limited (Japan), W. L. Gore & Associates Inc. (USA), Polartec, LLC (USA), Finetex EnE (South Korea), Stotz & Co. AG (Switzerland), Schoeller Textil AG (Switzerland), AkzoNobel N.V. (Netherlands), Sympatex Technologies GmbH (Germany).
Finally, you can see the projected value of the US WBFs market between 2014 and 2024. The figure below shows that the overall value of the market is expected to rise from $277.4 million to more than 460 million (66.7%) as ePTFE, PU, and polyester are the most used materials.
Figure 4: US Waterproof breathable market (in million U.S. dollars)
Functional outerwear must be waterproof for the maintenance of user comfort. Garments made of waterproof breathable fabrics shield from rain, snow, wind, and cold but allow for water vapor to be transferred from the inner to the outer environment in order to keep you warm and dry.
Performance composite fabrics prevail as the microporous membranes led by Gore-Tex dominate the market of waterproof breathable textiles today. The microporous film provides a barrier between your body and water droplets to give you protection from precipitation.
There are so many applications of waterproof breathable materials other than their traditional use in active sportswear for weather protection. They’re used in military, hospitals, construction, agriculture, transportation, and many other industries.
Keep in mind that waterproof fabrics are not perfect and they won’t work in all conditions. For example, in cold and wet weather, moisture vapor turns quickly to liquid water. This moisture accumulates in clothing and compromises the breathability and insulation capacity of your layered clothing system. WBFs have some limitations leading to customer dissatisfaction on certain occasions, however, they are an essential part of any amateur or professional outdoorsman’s gear.
* In J. Williams (Ed.), Waterproof and Water Repellent Textiles and Clothing, 2018, Elsevier Ltd.
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