The Rupp Report: Physiological Apparel Part IV: The Right Fabrics For Maximum Performance
Jürg Rupp, Executive Editor
One of the key factors of all functional apparel is the fabric, whether it is woven, knitted or warp knitted. The property of the fabric gives the final product its comfort and wearing performances. In the fourth round of its Physiological Apparel series, the Rupp Report highlights some fundamental characteristics and requirements of physiological apparel.
There are four different kinds of textile fabrics: wovens, knits, warp knits and nonwovens. According to their construction and finish, these fabric materials comply with the relevant apparel requirements.
For the understanding of the following fabric constructions, it is important to know that man-made fibers are produced as endless, so-called continuous filaments. Continuous filaments are basically flat, but, depending on the application, they can be treated by various methods such as texturing. Textured yarns are more bulky, more flexible and elastic, which is important, especially for knitted fabrics. Through the ongoing development of man-made fiber yarns, functional apparel could be improved significantly. Thanks to always finer yarns and surface treatments, coating with polyvinyl chloride (PVC) has largely been eliminated, with the exception of 100-percent waterproof fabrics.
Apart from fashionable aspects, woven fabrics for activewear mainly serve two functions: protection against wind and weather, and insulation. Thanks to their mostly dense construction, wovens usually perform better than knitted fabrics. Previously woven fabrics for weatherproof apparel were in most cases coated with PVC. The PVC coating ensures absolute waterproofness, but has a serious handicap: After a few minutes, the wearer feels like he is in a sauna — because the fabric can’t conduct air, the wearer sweats after a few minutes, and the body moisture cannot be transported to the outside. This coating corresponds to an airtight package and is normally applied only for heavy rainwear, the so-called oilskin. There are valuable alternatives, which will be discussed in the next installment of this series, which covers finishing.
Looking back to the yarns, thanks to the increasingly finer, microdenier yarns, many fabrics can be produced today that do not require additional coating for particular characteristics, but meet all the requirements for functional sportswear. They are wind- and waterproof, yet breathable. Why? Remember the Rupp Report about fibers and yarns (See "The Rupp Report: Physiological Apparel Part III: The Right Yarn For A Functional Product,” TextileWorld.com, August 5, 2014). Consider the filament bundle in the yarn, as in the example 167 f 48. There are 48 filaments in the yarn. If the yarn is 167 f 128, there are 128 individual filaments — the same yarn count, but the individual fibrils are finer, and consequently, the fabric is much denser with this yarn because the “space” between the fibrils is much smaller. Also, the surface area of the fabric is increased, and it can be expected that the moisture transfer proceeds through more fiber material with improved capillary action and good thermoregulation. In this fabric construction, water penetration is limited, but the body moisture can exhaust to the outside. It is scientifically proven that most moisture-transport mechanisms depend on the yarn and the fabric construction. With the same fiber material, one can produce suitable and efficient products, but also completely unsuitable products, if not all known requirements are taken into consideration.
In this context, especially concerning waterproofness, a new concept for activewear has emerged in the last 10 to 15 years: membranes. A lot of companies have claimed that their product is windproof, waterproof, and can even be breathable. Newark, Del.-based W.H. Gore & Associates Inc. was the first company to deal with membranes. The company started the business by producing artificial arteries and claimed that the polytetrafluoroethylene (PTFE) material would be suitable for functional activewear. Gore says it works; the Rupp Report says it doesn’t. The method to show how it works uses boiling water, which penetrates through the Gore membrane. But whose body moisture has a temperature of 212°F and the same partial pressure to penetrate through the membrane?
To give you, dear reader, an idea of what we are talking about, here are some numbers of diameters of molecules and pores in microns:
Knitted and warp-knitted fabrics have a great advantage compared with wovens: their elasticity. These fabrics mainly fulfill two important functions: to guarantee the unrestricted freedom of movement; and to transport body moisture to the next textile layer. Knitted and warp-knitted fabrics especially have made tremendous improvements. New combinations of materials, yarns and fabric constructions make knitted fabrics the ideal material for functionally correct activewear. Knitted activewear products mainly are worn directly against the body. Therefore, special attention must be paid to the chosen construction and the yarn. Of particular importance in this context is the skin-sensory behavior. Incorrect fabric construction can provoke uncomfortable sensations, such as itching, caused by the physical contact with the skin. Often, people talk about allergies when these sensations occur, which is completely wrong. This issue will be described when in the finishing installment.
Ideal Material: Double Jerseys
The ideal fabrics for truly physiologically correct activewear are double knits, also called double jerseys. The inside of the fabric is usually made of texturized filament or staple-fiber yarns, and the surface is made of natural fibers, mostly cotton. Why? The principle of all correct functional wear is the ability to transport the body moisture up to the next layer, which is in this case the surface of the double knit. The principle is very simple: the hydrophobic man-made fiber yarns transport the moisture by capillary action to the outside, where it is absorbed by the hydrophilic cotton. On the surface of the fabric, the moisture can evaporate. With this system, the wearer never feels wet and chilly. With this simple conclusion, the entire apparel physiology could be explained.
Last but not least, thanks to ongoing fast development, nonwovens are gaining ground in modern functional apparel. For activewear, they are used primarily as insulation or filling material. Tailor-made nonwovens can almost achieve the same properties as down, but are much cleaner and more easy-care. On top of that, the durability and resilience is much better. Also in the production of nonwovens, it is important to know that the finer the basic material of the nonwovens product, the better the insulation capabilities. And, nonwovens should always be made according to the same guidelines as other materials and provide the same unhindered moisture transport through the web to the next (outside) layer.
Man-made fiber nonwovens have further advantages compared to natural fillers such as down: even when wet, the air permeability and thermal insulation remains. A wet down fill insulation loses at least 50 percent of its isolation properties, which is higher than 25 percent of its own weight. In addition, these nonwovens dry very quickly. And, last but not least, the price of the filler plays an important role. Natural goose down is much more expensive. In the last few years, the price for down has soared. That’s why many producers replace the fillings with cheaper goose feathers or nonwovens. Sometimes the fillings in “100-percent” down jackets are stretched with goose feathers, which can cause big problems for the producers, if one thinks of the power of today’s social media.
August 19, 2014