Multi-Layer Fabrics: the art of weaving several layers in a fabric

New Architectural Approach to the Designing of multilayer fabrics by using various types of yarns to give desired apparel properties

Usually at least three layers are identified as follows:

• Inner Layer provides body comfort by keeping the skin dry. Also called base layer or first layer.
• Mid Layer provides warmth. Also called insulating layer.
• Outer Layer protects from wind and/or water. Also called outer layer which works as protection over the other two layers.

Often clothes combine two adjacent layers, as in the case of warm undergarments that provide both comfort and insulation.

The inner or base layer

The purpose of the inner layer is to draw the sweat away from the skin to the next layers, which makes the wearer feel warmer and more comfortable. The transfer of moisture happens due to capillary action, sometimes called wicking. The used materials are called wicking materials.

When moisture has moved from the skin into (nonabsorbent) clothing, it has more surface area and will evaporate faster. If a piece of clothing does not transfer moisture well, it is not strictly an inner layer garment at all, but simply a comfortable mid-layer garment.

• Wool is a combination of wicking and water-repelling properties and, along with silk, is the most expensive of the materials used for base layers. How comfortable wool feels against skin varies greatly, with Merino wool being softer. Wool is highly odor resistant.
• Synthetic materials such as Polyester, polyethylene, and microfiber-based fabrics are inexpensive. They have excellent water wicking properties.
• Wicking fabrics are modern technical fabrics which draw moisture away from the body. They are made of high tech polyester, which, unlike cotton, absorbs very little water. Cotton will absorb 7% of its weight in water, polyester only 0.4%. Cotton will, therefore, hang onto your sweat, making your garment heavy and unpleasantly clammy. Wicking polyester has a special cross-section and a large surface area, which picks up moisture and carries it away from your body, spreading it out, to evaporate easily on the outside of the fabric. So, you stay cool and dry. They can also carry specialist finishes, such as anti-bacterial agents which reduce odors, and insect repellent. However, in the absence of such anti-odor treatment, they quickly become notoriously foul-smelling. This is because their hydrophobicity causes them to strongly absorb the short-chain fatty acids that are responsible for body odor.
• Silk is expensive. It feels comfortable but is less warm, weaker and harder to take care of.
• Cotton is usually inexpensive. It absorbs moisture easily and is slow to dry out. When wet or damp, cotton loses its insulative abilities and becomes more thermally conductive than other materials. This makes it suitable for warm temperatures but potentially dangerous for cold and/or wet conditions. You will commonly hear that cotton is better forgotten because it is so cold when wet.

Mid Layer

The mid layer is needed in cold weather to provide additional insulation. The use of multiple thin layers facilitates adjustment of warmth. The mid layer should be more loose-fitting than the inner layer, as this leaves insulating air between the layers. However, if best possible moisture transfer is desired, too great a gap between any adjacent layers of clothing may reduce the moisture transfer by capillary action from one piece of clothing to another.

On the other hand, very loose-fitting layers can allow more removal of moisture (and heat) via air circulation. Capillary pressure is the main force responsible for the movement of moisture along or through a fabric, where the force of the surface tension between the liquid and the walls of a narrow gap or pore overcome the forces between the molecules of the liquid, moving it into empty gaps until the forces even out.

Permeability is the measure of a fabric’s ability to transport moisture through itself and is determined by a combination of sizes of spaces within it and the connections between the spaces.

• Wool is the traditional mid layer material with several good properties: it has good insulation even when wet, absorbs moisture but does not feel wet even when it holds significant moisture and transfers moisture.
• Fleece made from PETE or other synthetics has many of the features of wool but is lighter. It provides good insulation even when wet, absorbs very little moisture, and dries quickly. Although no longer commonly used in the industrialized world, natural sheepskin fleece could also serve the mid layer function.
• Down has a very good warmth: weight ratio, and can be packed down (squeezed) to take very little room. On the downside, it is expensive, makes a thick garment, dries slowly, loses its insulating properties when wet or compressed, and stops lofting properly after being washed several times.
• Synthetic Fiberfill such as Polyester fiber is used similarly to down but does not have as good a warmth: weight ratio. However, it is less expensive, provides better insulation when wet, dries quickly, and absorbs very little moisture. There are brands of very fine fiberfill like Thinsulate, PrimaLoft or Thermolite, that provides higher warmth for a given thickness.
• Cotton, as with the inner layer, is a cheap alternative, but a reasonable choice only when low insulation and moisture transfer is needed. Most people involved in outdoor activities would agree that cotton is a very poor material to wear in the outdoors because you MAY need to insulate yourself and unless you are not moving, you WILL need moisture transfer.

Outer Layer

Breathability

Some people will refer to wicking fabrics as being breathable – that is, they let air in and sweat out. Breathable showerproof and waterproof fabrics have tiny pores in the fabric, larger than water vapor molecules (so these can get out) but much smaller than drops of rain (so these can’t get in)

The outermost clothes are called the shell layer, but only if they block wind or water, or have good mechanical strength. Ideally, the shell layer lets moisture through to the outside (that is, is breathable), while not letting wind and water pass through from the outside to the inside. While this is enabled to some degree by modern materials, even the best and most expensive materials involve a slight trade-off between breathability and water- and wind resistance.

If heavy sweating is expected, one should avoid wearing any shell layer garments unless their protective properties are essential. For example, when one is jogging, no traditional shell layer is likely to be able to transfer enough moisture to keep the wearer feeling dry. But as more air permeable membranes emerge, when combined with pit zips the amount of moisture being transferred outwards would be sufficient for cardiovascular pursuits. As a general rule, one should consider using sufficiently warm mid-layer clothes.

Both “soft” and “hard” shell jackets and layers exist. Hard shells are commonly woven fabric and do not rip. Softshell may rip easier but are more flexible.

• Plastic raincoats protect completely from water and wind, but let through no moisture. To compensate for that, such raincoats usually have flap-covered holes and are very loose-fitting at the bottom to allow air circulation.
• Waterproof breathable (hard shell) materials are waterproof and somewhat breathable. Their essential element is a thin, porous membrane that blocks liquid water, but lets through water vapor (evaporated sweat). The more expensive materials are typically more breathable. The best-known brand is Gore-Tex, while one study shows that eVent, a newer material, has the best breathability, although it has less wind resistance.
• Water resistant (soft shell) most materials block water only partially, however as technology in the outdoor industry moves forward more fully waterproof soft shells are emerging such as Polartec neoshell or DryQ Elite. On the other hand, they are usually more breathable and comfortable, thinner, and cheaper than completely waterproof materials. Water-repellent coatings are often used. Before waterproof-breathable shells were invented, the “60/40” (60% cotton, 40% nylon) parka was widely used. Soft shells are not water “proof”.

The term soft shell is increasingly used to describe garments that combine partial or full water resistance with partial or full wind breaking ability. Softshell fabrics come in numerous varieties with many garments offering a combination, such as a wicking layer. In many cases, insulation is combined in an attempt to replace several layers with a single highly flexible one. One of the most unique characteristics of the woven softshell fabrics is the combination of wind-proofness, a high level of water resistance, and stretch — in many cases four-way stretch. Solid plastic films and micro-perforated laminates typically breathe much less and do not stretch at all.

Summary

The integration of performances in interactive textile fabric system has so far been rather complicated since they are based on multilayer or three-dimensional principles. These structures are today mainly put together by means of several processes, which is laborious and time-consuming. This has combined the principle of a three-dimensional multilayer weaving process and interactive textiles structures in order to enable the manufacturing of interactive textile structure in one process.

The process is using a manual reconstructed loom and the approach has been to use the 3D structures in order to integrate and organize conductive and compressive spacer layers as a textile capacitive structure. In this paper, it is seen that a three-dimensional structure enables the development of interactive textiles in one process. Future research will focus on developing other types of interactive structures.

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Acknowledgment:

Technical and technological Facts in this write up have been selected from various reputed sources. I do also acknowledge the research contents done by other research institutions and organizations.