1.0.Introduction:

Waterproof breathable fabrics are designed for use in garments that provide protection from the weather that is from wind, rain and loss of body heat. Clothing that provides protection from the weather has been used for thousands of years.The term 'breathable' implies that the fabric is actively ventilated. This is not the case. Breathable fabrics passively allow water vapour to diffuse through them yet still prevent the penetration of liquid water. Production of water vapour by the skin is essential for maintenance of body temperature. The normal body core temperature is 37C, and skin temperature is between 33 and 35C, depending on conditions. If the core temperature goes beyond critical limits of about 24C and 45 C then death results. The narrower limits of 34 C and 42C can cause adverse effects such as disorientation and convulsions. If the sufferer is engaged in a hazardous pastime or occupation then this could have disastrous consequences. During physical activity the body provides cooling partly by producing insensible perspiration. If the water vapour cannot escape to the surrounding atmosphere the relative humidity of the microclimate inside the clothing increases causing a corresponding increased thermal conductivity of the insulating air, and the clothing becomes uncomfortable. In extreme cases hypothermia can result if the body loses heat more rapidly than it is able to produce it, for example when physical activity has stopped, causing a decrease in core temperature. If perspiration cannot evaporate and liquid sweat (sensible perspiration) is produced, the body is prevented from cooling at the same rate as heat is produced. for example during physical activity, and hyperthermia can result as the body core temperature increases. If the body is to remain at the physiologically required temperature, clothing has to permit the passage of water vapour from perspiration at the rates under the activity conditions The ability of fabric to allow water vapour to penetrate is commonly known as breathability. This property should more scientifically be referred to as water vapour permeability. Waterproof breathable fabrics prevent the penetration of liquid water from outside to inside the clothing yet permit the penetration of water vapour from inside the clothing to the outside atmosphere.

2.0.Types of waterproof breathable fabric

There are several methods which can be used to obtain fabrics which are both breathable and waterproof. These can be divided into three groups:

Densely woven fabrics
Membranes
Coatings.

2.1.1. Densely Woven Fabrics:

Probably the first effective waterproof breathable fabric was developed in the 1940s for military purposes and is known' as Ventile.Ventile fabric was carefully engineered to make it effective1.The finest types of long staple cottons are selected so that there are very small spaces between the fibres. The cotton is processed into combed yarn, which is then plied. This improves regularity and ensures that the fibres are as parallel as possible to the yarn axis, and that there are no large pores where water can penetrate. The yarn is woven using an Oxford weave, which is a plain weave with two threads acting together in the warp. This gives minimum crimp in the weft, again ensuring that the fibres are as parallel as possible to the surface of the fabric.


When the fabric surface is wetted by water, the cotton fibres swell transversely reducing the size of the pores in the fabric and requiring very high pressure to cause penetration .The fabric is thus rendered waterproof without the need for any water-repellent finishing treatment.The military variants use thread densities as high as 98 per cm. Fabric for other applications uses much lower thread densities necessitating a water repellent finish to achieve the waterproof properties.Densely woven fabric can also be made from synthetic microfilament yarns. The individual filaments are less than 10 micrometer in diameter, so that fibres with very small pores can be engineered. Microfilaments are usually made from polyamide or polyester. The latter is particularly useful as it has inherent water-repellent properties. The water penetration resistance of the fabric is improved by application of silicone or fluorocarbon finish Although fabrics made from microfilaments have a soft handle many of them are windproof, but not truly waterproof as the synthetic filaments do not swell when wet. The use of very fine fibres and filaments and dense construction results in fabrics with very small pore size compared with conventional fabrics. Typical pore size for a waterproof fabric is about 10 micrometer compared with 60 micrometer for conventional fabric. Ventile fabric has a pore size of about 10 micrometer when dry and 3-4 micrometer when wet2. Fabric made from microfilaments is claimed to have up to 7000 filaments per centimetre. The military variant of Ventile fabric has about 6000 fibres per centimetre.

2.1.2. Membranes

Membranes are extremely thin films made from polymeric material and engineered in such a way that they have a very high resistance to liquid water penetration, yet allow the passage of water vapour. A typical membrane is only about 10 micrometer thick and, therefore, is laminated to a conventional textile fabric to provide the necessary mechanical strength. They are of two types, microporous and hydrophilic

2.1.2.1. Microporous Membrane

The first and probably the best known microporous membrane developed and introduced in 1976 by W.Gore,is known as Gore-Tex.This is a thin film of expanded polytetrafluoroethylene (PTFE) polymer claimed to contain 1.4 billion tiny holes per squaremeter.The holes are much smaller than the smallest raindrop (2-3 micrometer compared with 100 micrometer)3 yet very much larger than a water vapour molecule. Other manufacturers make similar membranes based on microporous polyvinylidene fluorIde (PVDF) cast directly on to the fabric4. The hydrophobic nature of the polymer and small pore size requires very high pressure to cause water penetration. Contamination of the membrane by various materials including body oils, particulate dirt, pesticide residues, insect repellents, sun tan lotion, salt and residual detergent and surfactants used in cleaning' have been suspected of reducing the waterproofing and permeability to water vapour of the membrane. For this reason microporous membranes usually have a layer of hydrophilic polyurethane to reduce the effects of contamination5.

2.1.2.2. Hydrophilic Membranes

Hydrophilic membranes are very thin films of chemically modified polyester or polyurethane containing no holes which, therefore, are sometimes referred to as non-poromeric. Water vapour from perspiration is able to diffuse through the membrane in relatively large quantities. The polyester or polyurethane polymer is modified by incorporating up to 40% by weight of poly(ethylene oxide)2.The poly(ethylene oxide) constitutes the hydrophilic part of the membrane by forming part of the amorphous regions of the polyurethane polymer system. It has a low energy affinity for water molecules which is essential for rapid diffusion of water vapour6. These amorphous regions are described as acting like intermolecular 'pores' allowing water vapour molecules to pass through but preventing the penetration of liquid water owing to the solid nature of the membrane

Methods of Incorporation

Membranes have to be incorporated into textile products in such a way as to maximize the high tech function without adversely affecting the classical textile properties of handle , drape and visual impression3.There are four main methods of incorporating membranes into textile products.The method employed depends upon cost,required function and processing conditions3:

a) Laminate of membrane and outer fabric :
The membrane is laminated to the underside of the outer fabric to produce a to layer system.This method has the disadvantage of producing a rustling, paper like handle with reduced aesthetic appeal but have advantage of very effective protective properties of wind resistance and water proofing.This method is mainly used for protective clothing

b) Liner or insert processing:
The membrane is laminated to a light weight knitted material or web.The pieces are cut to shape from this material, sewn together and the seams rendered waterproof with special sealing tape. This structure is then loosely inserted between tite outer fabric and the liner. The three materials (outer, laminate and lining) are joined together by concealed stitch seams. If high thermal insulation is required, then the lightweight support for the membrane is replaced by a cotton, wool or wadding fabric. This method has the advantage of giving soft handle and good drape. The outer fabric can also be modified to suit fashion demands.

c) Laminate of membrane and lining fabric:
The laminate is attached to the right side of the lining material. The functional layer is incorporated into the garment as a separate layer independent of the outer fabric. This method has the advantage that the fashion aspects can be maximized.

d) Laminate of outer fabric, membrane and lining:
This produces a three-layer system,which gives a less attractive handle and drape than the other methods and, therefore, is not commonly

2.1.3. Coatings

These consist of a layer of polymeric material applied to one surface of the fabric. Polyurethane is used as the' coating material. Like membranes, the coatings are of two types; micro porous and hydrophilic. These coatings are much thicker than membranes. Contains very fine interconnected channels, much smaller than the finest raindrop but much larger than a water-vapour molecule

2.1.3.1. Micro Porous Coatings

Wet Coagulation

Polyurethane polymer is dissolved in the organic solvent dimethyl formamide to produce a solution insoluble in water. This is then coated on to the fabric. The coated fabric is passed through a conditioning chamber containing water vapour. As the organic solvent is miscible with water, it is diluted and solid polyurethane precipitates. The fabric is then washed to remove the solvent, which leaves behind pores in the coating. Finally the coated fabric is mangled and dried. This method is not very popular as it requires high capital cost for machines and solvent recovery is expensive.

Thermocoagulation

Polyurethane is dissolved in an organic solvent and the resulting solution mixed with water to produce an emulsion. The emulsion 'paste' is coated on to one side of the fabric. The coated fabric then goes through a two-stage drying process. The first stage employs a low temperature to remove the organic solvent, precipitating the polyurethane. The coating is now a mixture of solid polyurethane and water. The second stage employs a higher temperature to evaporate the water leaving behind pores in the coating.

Foam Coating

A mixture of polyurethane and polyurethane/polyacrylic acid esters are dispersed in water and then foamed. The foam is stabilised with the aid of additives. The foam is then coated on to one side of the fabric. The coated fabric is dried to form a micro porous coating. It is important that the foam is open cell to allow penetration of water vapour but with small enough cells to prevent liquid water penetration. The fabric is finally calendered under low pressure to compress the coating. As the foam cells are relatively large, a fluorocarbon polymer water-repellent finish is applied to improve the water-resistant properties. This type of coating production is environmentally friendly as no organic solvents are used.

Hydrophilic Coatings

Hydrophilic coatings5 use the same basic water vapour permeability mechanism as the hydrophilic membranes. The difference between microporous materials and hydrophilic materials is that with the former, water vapour passes through the permanent air-permeable structure whereas the latter transmit vapour by a molecular mechanism involving adsorption-diffusion and desorption. These coatings are all based on polyurethane, which has been chemically modified by incorporating polyvinyl alcohols and polyethylene oxides. These have a chemical affinity for water vapour allowing the diffusion of water vapour through the amorphous regions of the polymer.The balance between hydrophilic and hydrophobic" components of the polymer system has to be optimised to give acceptable vapour permeability, flexibility, durability and insolubility in water and dry cleaning solvents.

Swelling of the membrane is encouraged to assist water vapour diffusion yet it also has to be restricted to prevent dissolution or breakdown in water or in the other solvents with which the polymer is likely to come into contact. Poly (ether-urethane) coatings and membranes have excellent integrity. This can be conferred in two ways:

1 by a high degree of hydrogen bonding, principally between polar groups in the hydrophobic segments of adjacent polymer chains
.
2 by forming covalent crosslinks between adjacent polymer chains. The effective length and density of the crosslinks are variables affecting polymer swelling and thus vapour permeability.

Methods of Applying Coatings

The conventional method of applying coatings to fabric is to use direct application using the knife over roller technique3. The fabric is passed over a roller and liquid coating is poured over it. Excess liquid is held back by a 'doctor blade' set close to the surface of the fabric. The thickness of the coating is determined by the size of the gap between the blade and the surface of the fabric. The coated fabric is passed through a dryer to solidify the coating. Sometimes the coating is built up in several layers by a number of applications. In order to achieve thinner coatings and, therefore, more flexible fabric and to apply coating to warp knitted, nonwoven, open weave and elastic fabric, transfer coating is used. The liquid coating is first applied to a silicone release paper using the knife over roller technique. This is then passed through an oven to solidify the coating. A second coating is then applied and the textile fabric immediately applied to this. The second coating, therefore, acts as an adhesive. This assembly is passed through an oven to solidify the adhesive layer. The coated fabric is stripped from the release paper, which can be reused.

3.0 Various Commercial Water Breathable Fabric

Breathable Membranes

All breathable microporous membranes comprise an extremely thin man-made film whose physical structure contains microscopic pores that are large enough for water vapour (perspiration) to pass through but small enough not to let water droplets through. Thus the membrane is breathable, waterproof and windproof. Modern microporous membranes are usually laminated to a face fabric, and available in two and three layer versions.

Gore-Tex

Gore-Tex is a unique wafer thin microporous membrane, which contains over 9 million pores per square inch. Each pore is 20,000 times smaller than a water droplet, yet some 700 times bigger than a moisture vapour molecule. This gives the fabric the excellent levels of waterproofness and breathability that the brand is famous for.

Gore-Tex is a bi-component membrane, meaning that it is made up of two parts. The main part is made from expanded polytetrafluoroethylene. This is then combined with an oleophobic (oil hating) layer that protects the membrane from the natural oils that the human body emits, insect repellents, cosmetics etc. The outer face of the Gore-Tex fabric is coated with a hydrophobic DWR (Durable Water Repellency) treatment which encourages surface water to bead up and run off, improving the wet weather performance of the garment and promoting breathability by preventing wetting-out of the outer face. There are a number of different Gore-Tex constructions currently used within the industry:

Classic 2-Layer

Provides soft, versatile weather protection and is good for end uses such as walking, streetwear, golf and skiing. Made by laminating a nylon or polyester face fabric to the Gore-Tex membrane and then hanging a mesh lining just inside the laminate.

Classic 3-Layer

Designed for ultimate durability in rugged use applications in tough weather conditions such as high altitude mountaineering. Made by again laminating a face fabric (usually nylon) to the Gore-Tex membrane, an inner protective mesh scrim is then laminated to the other side of the membrane, giving better durability.

Paclite

Lightweight and more packable than either two or three layer garments, designed for ultra light mountaineering or other fast moving sports. As with two layer garments, the face fabric is bonded to the Gore-Tex membrane, but unlike either of the other constructions, abrasion resistant raised nubs (or dots) protect the membrane. This means that as there is less between you and the membrane, breathability is increased.

XCR

Standing for eXtended Comfort Range, XCR is the new product from Gore-Tex, which by using new membrane technology and new lamination techniques offers 25% more breathability than classic Gore-Tex garments. Designed for mountaineers, backpackers, snowboarders, backcountry skiers and other outdoor enthusiasts who value performance and demand the most from their gear. Available in both two and three layer construction.

Hydro Dry P3 (Sprayway)

The top fabric in the Hydrodry range from Sprayway, P3 has a hydrostatic head of 10,000mm. It is waterproof and has a good level of breathability. Again developed from a hydrophilic laminate, Hydrodry P3 is available in both 2-layer and 3-layer constructions. Hydrodry P3 provides Sprayway customers with a technical alternative to Gore-Tex in the same way that Drilite Extreme does for Mountain Equipment.

Drilite Extreme or DLE (Mountain Equipment)

A new development from Mountain Equipment, Drilite Extreme is a monolithic, hydrophilic laminate, with a hydrostatic head of more than 20,000mm. DLE (Drilite Extreme) is totally waterproof & exceptionally breathable, guaranteed. An added benefit of hydrophilic laminates is Drilite Extremes elasticity, making it especially ideal for stretch panels in the knees and seat areas, guaranteeing the highest freedom of movement and comfort. Available in 2 and 3 layer contructions.

HyVent (The North Face)

Designed as an innovative option for complete weather protection, HyVent is a waterproof/breathable polyurethane-based membrane. While it is slightly less breathable than Gore-Tex laminates it is extremely waterproof, and can be counted on as a dependable protective outer layer. This combination of high waterproofness and breathability makes it ideal for keeping the elements out.

To increase the comfort and breathability level of the coating, TNF have developed precise custom lining options in both their 2- and 3-layer versions of the HyVent technology.

eVENT (Pearl Izumi/Rab/Montane)

eVENT Fabric is a Direct Venting waterproof barrier. Using a proprietary and patent-pending Dry System technology, eVENT Fabric has set a new standard for comfort by allowing perspiration to dissipate and vent before it saturates the inside of the fabric. At the core of eVENT fabric is hydrophobic ePTFE (expanded Polytetrafluoroethylene) film that has been rendered oleophobic, and thereby free from body oil contamination, via a method that retains the inherent open-pore structure of the membrane.

Breathable Coatings

All coatings are created by spreading a thin layer of resin directly onto to the inside face of the chosen fabric. Two distinct types of breathable coating exist: microporous and hydrophilic.A microporous coating works on the same principle as a microporous membrane, the pores in the coating being large enough to let water vapour pass through but small enough to keep water droplets out. Hydrophilic coatings rely on the chemical and molecular properties of water molecules. The heat that the body generates inside the garment drives water vapour (perspiration) down the polymer chains found in the coating to the external face, the water vapour moving from molecule to molecule rather than freely through a physical hole or pore. As the body produces more moisture and the fabric gets wetter, the chains naturally increase in size, allowing even more moisture movement.In use, both types of coatings are effective, with the overall performance of any garment being determined by a combination of factors such as the choice of face fabric, use of a separate lining, and the general design, cut and finish of the garment.

Triple Point Ceramic (Lowe Alpine)

Triplepoint Ceramic is a unique multi-layer microporous coating which is waterproof, windproof and breathable. It differs from other treatments in that the manufacturing process involves multiple coatings and the introduction of ceramic particles, which are impregnated into the coating under high pressure.
This has the effect of creating microscopic holes around each particle. These cavities are large enough to permit the passage of water vapour to the outside face but small enough to prevent liquid water from moving the other way. Since the Triplepoint Ceramic coating is physically anchored to the fabric it wont de-laminate or become damaged. This construction is what makes the fabric inherently windproof as well as highly breathable and waterproof. A special Dry Yarn technology DWR treatment is also applied to the coated fabrics outer face to significantly improve wet weather performance and beading, (this can be re-generated simply by exposing the garment to a direct heat source i.e. medium heat iron or tumble drier). There are currently two constructions of Triplepoint Ceramic used in garment production.

Standard

The fabric is constructed and coated as described above and a free hanging Dryflo mesh lining is then added to protect the coating, and to help disperse any condensed water droplets on the inner face of the garment.

Direct Lined

Triplepoint Ceramic Direct Lined is a new fabric combination for the Alpine Pro range . Unlike the standard construction, a fixed lining is applied directly to the Triplepoint Ceramic coating. This gives better performance when combined with a high spec. face fabric.

Triple Point (Lowe Alpine)

A multi-layer non-ceramic coating which is lighter than Triple Point Ceramic and therefore better suited to general walking/outdoor activities rather than more demanding outdoor sports. The outer face of the fabric has a standard DWR treatment applied to it to enhance wet weather performance.

Hydrodry P2 (Sprayway)

A more basic version of Sprayways Hydrodry P3, Hydrodry P2 is a mixture of hydrophilic coatings and laminates rather than a laminate outright. With a lower hydrostatic head (5,000mm) than P3 and a slightly lower degree of breathability, Hydrodry P2 is pitched at the more general walking market. Available only in the equivalent of a two-layer construction, Hydrodry P2 is a good competitor to standard Triplepoint and Aquadry.

Entrant II

A microporous coating with a multi-layer structure. Applied to a suitable face fabric it has good waterproof and breathability characteristics. Entrant II is used on some F&T nylon face fabrics to enhance performance and durability.

Aquadry

Aquadry is Craghoppers own hydrophilic coating. Constructed and working in a very similar way to Sprayways Hydrodry P2, Aquadry is a good choice fabric for a middle of the range waterproof garment- it is waterproof (at least 7,000mm), windproof and breathable. The Aquadry label carries a hydrostatic head measurement (in meters) and a breathability rating (%age) on each garment.

HPX Technology

The fabric allows moisture vapour from inside the suit to breathe out, whilst stopping any sea or rainwater getting in. This is achieved by having microscopic holes in the membrane, large enough to let water vapour out, but much too small to let water droplets in. Incorporated into the HPX Jacket and Smock is Stretch HPX fabric which is exclusive to Musto. Stretch HPX uses a stretch GORE-TEX Ocean Technology membrane in a three layer laminated fabric. This revolutionary fabric has an elasticity of 30%. The result is the least restrictive, most breathable fabric for foul weather gear available.

GORE Windstopper Fabric

This is a windproof and breathable microporous ePTFE membrane which is laminate to a second fabric such as a fleece to form a very breathable & durably windproof barrier. Windstopper garments provide up to 2 times more thermal insulation than conventional non-laminated garments.

MPX GORE-TEX Technology

The fabric allows moisture vapour from inside the suit to breathe out, whilst stopping any sea or rainwater getting in. This is achieved by having microscopic holes in the membrane, large enough to let water vapour out, but much too small to let water droplets in. Laminated to the GORE-TEX membrane are inner and outer fabrics. The outer fabric is a hardwearing woven nylon to give the overall fabric the strength that is required. MPX GORE-TEX products are ideal for offshore and coastal racing and cruising. MPX GORE-TEX Race is ideal for high activity, high performance sailing such as racing round the cans.

GORE-TEX Fabric Technology

The original breathable GORE-TEX fabric uses the standard GORE-TEX membrane. Weve bonded an outer layer of durable, woven nylon to it and created a material thats an excellent choice for the shell of Middle Layer garments.

Waterproof & Showerproof Breathable Fabrics

This chemical process is helped by a pressure difference, which drives the water vapour from the high pressure inside the clothing system, to the low pressure outside. While not as efficient or as durable as GORE-TEX fabric, hydrophilic fabrics do offer a lower price point. Breathable waterproof fabrics have taped seams, thus making them fully waterproof for coastal, inshore and dinghy sailing, as well as onshore use.

POLARTEC Fabrics

Polartec Classic 100

Polartec Classic 100 stretch fabric is an expedition weight fabric for use in HP (High Performance) thermal underwear.

Polartec Classic 200

Polartec Classic 200 is a mid-weight fabric used in the Polartec Middle Layer, the Snug Shirt and the lining for the Snug Jackets and GORE-TEX fabric Middle Layer.

Polartec Thermal Pro

Polartec Thermal Pro features in our Snug Mock Wool garments giving the ultimate warmth for weight, with increased wind resistance and a DWR finish (Durable Water Repellency), which causes water to bead and run off the surface.

3Layer System, Yachting

To keep warm in the worst conditions first of all you must stay dry. To do this your clothing must transport body moisture away from the skin, hold dry warm air close to the body & keep rain and snow out. Thats what Mustos 3 Layer System does, in three lightweight, non-restrictive layers.

Layer 1 - The Base Layer

This layer is worn next to your skin and must transfer (wick) sweat away from your body as fast as possible. Polyester fabrics are best for this. Beware of cotton clothing which can absorb 30 % more than its weight in water and transfers heat away from your body thirty times quicker than dry air. Mustos Thermals absorb less than 0.5% of their weight in water.

Layer 2 - The Middle Layer

The main job for the mid-layer is to hold warm dry, insulating air inside the clothing system and close to the body. It must also continue the transmission of water vapour through the clothing system as started by the base layer. Mustos Middle Layer WINDSTOPPER and Middle Layer GORE-TEX garments are great for this job.

Layer 3 - The Outer Layer

The third layer is completely waterproof to the outside elements. It must also stop the wind whipping away the precious warm, dry air that is held inside. But the third layer must also deal with the moisture that is transmitted outwards by the inner two layers. This is where breathable waterproof fabrics come in. They continue the transmission of the water vapour through the outer layer all the way to the outside environment.

CONCLUSION

Water proof breathable fabric are designed to provide protection from the wind, rain and loss of body heat. The breathable fabric passively allows the water vapour and prevents the penetration of liquid water for comfort clothing. The breathable are very much better than fabric coated with conventional water proof materials, which have a higher resistance to vapour transport than ordinary woven and knitted apparel fabric. The water proof breathable fabric continues to breathe under rainy condition. However the breathability of most of them ultimately ceases after long exposure to prolonged severe rainy condition. The water proof breathable fabric is highly breathable, too , keeping you dry and comfortable whatever your activity.

REFERENCES

1.Ventile Technical Literature, Harris Watson Investments Ltd, Talbot Mill, Froom Street, England.

2.Gr Lomax Textiles, 1991, No:4, 12.

3.W Mayer, U Mohr And M Schuierer,Int. Textile Bull, 1989,No:2,18.

4.Anon, Design News, 1988,44,No:13(July )48.

5.J Lomax,Coated Fabrics,1990 20(October)88.

6.W O Lotens, What Breathability Do You Need Symposium, June 1991

7.David A Holmes, Water Proof Breathable Fabrics.

About the author:

R.PERUMALRAJ did his M.Tech from theTextile Technology Department of PSG.COLLEGE OF TECHNOLOGY after completion of B.Tech. in Textile Technology(1983) from PSG.COLLEGE OF TECHNOLOGY. He is having around 12 years of working experience in Research & Development, and Teaching.

R.PERUMALRAJ is presently working as a Senior Lecturer in Department of Textile Technology, bannari Amman Institute of Technology He has around 20 publications in reputed national and international textile journals, various national and international conferences.

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