Waterproof breathable fabrics and materials have been a part of our lives for around 40 years. But how much do you really know about them? This article aims to introduce you to the world of waterproof breathable fabrics and clothing, familiarizing you with their properties, applications, and the current trends in the WBFs market.
In inclement weather, your outerwear must be windproof and waterproof, as it is expected to provide protection against both wind and precipitation. The waterproof material is designed to fully shield you from rain, snow, and wind by preventing the penetration and absorption of liquid water. Typically, waterproof textiles act as a barrier between your body and the environmental humidity. While waterproof fabrics offer excellent protection from the elements, they are unable to effectively transport the perspiration from the inside of the clothing to the outside, potentially causing moisture buildup and making the wearer feel damp.
One possible solution to this problem is provided by the so-called waterproof breathable fabrics (WBFs). The technology for manufacturing waterproof breathable textiles has been continuously developing and improving since the introduction of Gore-Tex in the 1970s. It is also quite diverse, with numerous new fabrics being introduced through a combination of innovation and evolution. Garments made of waterproof breathable textiles are utilized by sports and outdoor enthusiasts as well as professionals in any weather 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.
Table of Contents
Types of waterproof breathable fabrics
The classification of waterproof breathable fabrics is based on two criteria:
- The structure of the waterproof-breathable layer.
- The technique used for developing WBF.
Waterproof breathable fabrics (WBFs) can be categorized into three main types based on their structure. The first type is a tightly woven fabric made of long fiber cotton, which allows minimal gaps and provides breathability. The second type is microporous, either laminated or coated, featuring very small gaps throughout the fabric that allow water vapor to escape while preventing water from permeating from the outside. The third type is composed of nonporous structures and is developed as hydrophilic films. These films absorb water vapor on one side and re-evaporate it from the other side, effectively preventing liquid water penetration. Other types of WBFs are usually combinations of two or more of these structures.
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 can evaporate through the pores since they are larger than vapor molecules. The diameter of a water vapor molecule is 40×10⁻⁹ mm, whereas the diameter of various drop types is much larger as shown in Table 1.
Microporous membranes and coatings function well when the pores on the outer surface of the fabric are no larger than 0.0002-0.0003 mm, which is equivalent to 2-3 μm. Meanwhile, the average pore size in microporous membranes typically ranges from 0.0001 to 0.005 mm (1-50 μm). Generally, water vapor transmission depends on the size and thickness of pores, as a decrease in pore size and thickness increases 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) to enhance its waterproofness. The reason is quite obvious: the pore structure should prevent water droplets from permeating through the fabric from the outside. Meanwhile, characteristics such as fiber fineness, inherent moisture absorption, and the ability of the fiber to swell with increasing moisture content are other important features of tightly woven fabrics.
The first type of such structure is called Ventile, which is made of high-quality long staple cotton fibers (fine Egyptian cotton) and was introduced in England during WW2. How does it work? The main principle is simple. When the fabric is dry, it’s highly breathable due to the open structure of the cotton fibers. 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 under very high water pressure. For better results, the densely woven fabric is impregnated with a DWR to minimize further penetration.
|Need a tough outdoor jacket suited for changing weather? Then, why not look for a jacket made with cotton fabric?
Designed for a great outdoor experience, the Orvis Heritage Field Coat is lightweight, durable, almost completely silent, and can be adapted depending on the weather conditions. The cut of this beautiful jacket is between classic country styling and modern-day design. This coat is not cheap by any means but you get a lot of bang for the buck – it’s a total game-changer for various country pursuits such as hunting, fishing or backpacking in changing weather conditions.
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.
An interesting example is a Swedish company – Fjallraven. They make many of their products (jackets, pants, backpacks, etc.) from a densely woven fabric called ‘G-1000‘. The fabric, a combination of 65:35% polyester and cotton, is treated with Greenland Wax for added water resistance. Fjallraven produces eco-friendly garments that are PFC-free (PFC stands for Perfluorocarbons – chemicals used as DWRs). Well, we should mention that they are not entirely PFC-free because of the zippers. Note that the products made from the G-1000 fabric are breathable and highly water-resistant but not waterproof. Nevertheless, Fjallraven’s jackets and pants are excellent for a variety of climatic conditions, including wind, light rain, and snow.
Materials that have a solid polymer-based film or coating (with high resistance to water penetration) are also used. Thin hydrophilic films are commonly utilized, as the permeability of water vapor through such films depends on their thickness. Thicker hydrophilic films tend to be more permeable to liquids.
The transmission of moisture vapor is achieved through molecular diffusion, where moisture is absorbed by the hydrophilic membrane or coating, diffused through the film, and released on the other side. This process is illustrated in the figure below. The Sympatex membrane is a notable example of this type of waterproof breathable fabric. The membrane is climate-neutral, fully recyclable, and does not contain PTFEs or PFCs. The German brand Sympatex has gained popularity among sports and protective workwear brands due to its excellent high-tech functionality and environmentally friendly technology. Understandably, Sympatex is much more popular on the European market for waterproof breathable clothing and footwear. There is a wide range of premium outdoor products equipped with the Sympatex membrane. Among them:
- Hiking boots
- Work boots
- Ski and snowboard gear
- Cycling equipment
- Waterproof gaiters and shoe covers
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 typically contain approximately 1.2-1.4 billion tiny holes per square centimeter. These pores are considerably smaller than the smallest raindrops and generally range between 0.1 and 10μm (1 mm = 1000 μm). However, they’re larger than water vapor molecules, allowing them to pass through the membrane’s pores. 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 under certain circumstances (such as prolonged exposure to severe rainy conditions), breathability can be significantly reduced or even completely inhibited. 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 contrasting effects on the water vapor transfer rate of the fabric: wind tends to increase it, while rain tends to decrease 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 seal the surface pores, reducing the risk of contamination of the microporous layer by particles like dust, detergents, pesticides, etc. A hydrophilic finish, often achieved by chemically modifying PU or polyester with poly(ethylene oxide) on a microporous structure, is utilized to improve the water-resistance of microporous coatings. This ensures enhanced waterproofing capabilities while still allowing water vapor molecules to pass through.
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 has 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 a temperature-dependent response, adaptive insulation inspired by penguins in extreme cold conditions, and water-repellent fabrics based on superhydrophobicity or the lotus leaf effect (where water beads up and rolls off, cleaning the surface) are just a few examples of biomimetic projects in the realm of 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, relies on relative humidity levels. If the humidity inside the jacket is higher than outside, moisture will tend to move outward to establish equilibrium. Conversely, if the ambient environment is more humid than the interior of 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 treatment must keep the face fabric drier than the inner side, enabling 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 the 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.
There are two main functions of waterproof breathable materials: waterproofness and breathability. Waterproofness refers to a material’s ability to resist the penetration of water, while breathability refers to the capacity of a fabric to allow water vapor to pass through. As total waterproofing and total breathability are mutually exclusive ideas, the concept of waterproof breathable fabrics involves a 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 provide complete protection from the elements only if its seams, zips, joints, and pockets are also waterproof. The number of openings through which water can penetrate should also be minimal. This ensures 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. Generally, breathability or water vapor permeability ensures improved microclimate and thermal comfort.
The most common method of measuring the 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. Generally, a fabric with a water column measurement of at least 5000 mm is considered truly waterproof, although some manufacturers may have a minimum requirement as low as 1000 mm.
Table 2: Fabric waterproof ratings
Many people wonder what fabric breathability means. While it 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. A breathable fabric enables perspiration to be transported from the skin to the outside of the garment, ensuring comfort for the wearer and preventing moisture buildup on the inside. 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 like waterproofness ratings, manufacturers employ different methodologies and tests to determine the breathability of the fabric. It is important not to blindly accept the ratings provided by producers for their outdoor products. Their main goal is to promote more sales so mannufacturers have a serious reason to inflate the ratings of their products.
Table3: Fabric breathability ratings
WBFs find extensive use in the clothing industry, particularly in sportswear, workwear, and leisurewear. While functionality is a key consideration, it must be balanced with subjective and objective features, including style, quality, comfort, weight, and price. The importance of one (or more) of the aforementioned features can vary from the most important feature to a completely irrelevant one depending on the specific outdoor activity. Additionally, the choice of colors can play a significant role. Users engaged in forestry, fishing, and hunting often prefer camouflage patterns or muted colors, while professionals such as policemen, firefighters, and construction workers rely on brightly colored garments such as yellow, orange, and red. Waterproof breathable jackets, parkas, rain pants, hats, gloves, socks, and shoes are among the most popular products on the WBFs market. Some of the best poncho designs are also crafted from waterproof breathable textiles. 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, and 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 backpack 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, drysuits, sleeping bag covers, repair sheets, 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
Trends in the waterproof and breathable textiles industry
It is a thriving 2 billion-dollar business (with $1.83 billion in 2022, where membrane products account for 74.3%). Market research and management consulting companies like Grand View Research Inc. and Global Market Insights Inc. predict further expansion, with a compounded annual growth rate of between 5.5% and 6% in the coming years until 2030 (to nearly $3 billion). There are numerous reasons for this, with the main ones being: 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.
While Europe has historically held a significant market share in the waterproof and breathable textiles industry, the Asian market, particularly China, has experienced substantial growth in recent years. The Asia-Pacific region, including China, is now considered one of the fastest-growing markets for waterproof breathable clothing and footwear. Major players in the industry still come from the US, Europe, and Asia, but the production landscape has shifted. Many manufacturers now predominantly produce in Asian countries such as China, Taiwan, South Korea, and Thailand due to lower costs and increased competition. This shift has also contributed to a global decrease in fabric and finished garment prices.
Market leaders include companies like Toray Industries Inc. (Japan), Teijin Limited (Japan), W. L. Gore & Associates Inc. (USA), Polartec, LLC (USA), Schoeller Textil AG (Switzerland), and Sympatex Technologies GmbH (Germany). These companies are well known for their advanced technologies and products in the field of waterproof and breathable textiles.
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 to ensure user comfort. Garments made of waterproof breathable fabrics protect against rain, snow, wind, and cold while allowing water vapor to escape from the inner environment to the outer, keeping you warm and dry.
Performance composite fabrics, led by Gore-Tex and its microporous membranes, dominate the market of waterproof breathable textiles today. The microporous film acts as a barrier between your body and water droplets, providing protection from precipitation.
There are numerous applications of waterproof breathable materials beyond their traditional use in active sportswear for weather protection. They are utilized in the military, hospitals, construction, agriculture, transportation, and various other industries.
Keep in mind that waterproof fabrics are not perfect and do not work in all conditions. For instance, in cold and wet weather, moisture vapor can quickly condense into liquid water, leading to accumulation in clothing and compromising 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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