July 11, 2005

Tech For Comfort 

I really want to write a piece lighter and more technology-orinted, after the atrocity of last week. As I already said, while focusing on the enemy is important not to lose sight of what we are fighting for.

Synthetic fibers are far superior to natural ones in many regards. Polyester, nylon, polypropylene, UHMWPE1 fibers (not to mention high-performance aramids such as Kevlar) have much higher tensile strength and abrasion resistance than even the best natural fibers. I have a pair of combat trousers made of cotton/polyester fabric (nothing high-tech), and after a couple of years of use they show no noticeable wear. The high-performance fabric Cordura® is extremely resistant to abrasion. High tensile strength fibers are what allows the manufacture of effective but (relatively) light and comfortable body armor.

Fabric made from synthetic fibers are also virtually inattacable by bacteria and fungi, and have the benefit of drying faster. And, unless they are badly abused (for example washing at too high temperature), synthetic fibers will conserve their properties for all the lifetime of the garment. There is a downside, of course: generally natural fibers are more heat resistant.

Natural fibers have a fixed chemical composition, and come in the form of filaments of a certain size and length that cannot be altered. The composition of polymers instead can be fine-tuned with the addition of co-monomers, and it is quite easy to spin fibers in a variety of diameters to satisfy different applications. I have seen hollow-fiber polyester for enhanced thermal insulation, also.

A rather recent innovation is microfiber: polyester most often, spun in very thin filaments. These fibers can be woven in classical patterns, producing fabric with interesting properties: they are soft and elastic, warm and comfortable to wear. Microfiber cleaning cloths perform much better than cotton ones: a microfiber cloth used only with water cleans window panes as well as a cotton one with detergent. It will also absorb a considerable amount of water, but release most of it remaining just moist simply by wringing the cloth. A fast-drying fabric is a considerable improvement for home and industrial washing, but it can become of paramount importance for outdoor clothing. If you have ever had to wear damp clothes, you know what I mean.

But microfiber can also be wowen in more elaborate patterns: a leading producer of sportswear has t-shirts made of fabric with a grid of tiny holes, which greatly facilitate the evaporation of sweat. Even more elaborate, there is a fabric that is smooth and tight on one side, but has lots of tiny bumps on the skin side: these bumps keep the fabric away from the skin, creating a layer of rather stationary air. This layer allows sweat to evaporate without soaking the fabric, but also constitutes a stable micro-climate that will keep one comfortable in a wide range of situations and even reduce winchill. It was a cool spring afternoon swept by a northerly wind, and I felt perfectly comfortable wearing only one of such T-shirts, while my mates all had tees and jackets.

Another family of high-performance fabrics is Gore-Tex®: these are not exactly woven fibers, but rather membranes of microporous PTFE2. These membranes give outstanding protection from water and windchill, but are also breathable, light, thin and flexible. I have a Gore-Tex lined jacket, and while it is not particularly warm (being very thin), no wind can get through it, absolutely. These membranes have been used in extreme conditions, like spacesuits and military gear - you can't drop off battle when the weather gets rough, so all-weather garments are important for soldiers. Especially waterproof boots, because wet feet can easily suffer hypothermia and a lot of other unpleasant consequences.

The point is, no natural fibers have these properties, no way. Leather stops wind too, but is not as breathable, and often is heavy and scarcely flexible. And all-natural types often do not like the idea of using leather. It is true that animals are often well adapted to extreme environments, but it's the whole of the animal to be adapted, not only its fur or feathers. For example, polar bears have a thick layer of fat underneath their skin, and that provides most of the thermal insulation they need, not the fur.

And watch out for when advance of material science and nanotechnology will provide active fabrics, capable of adapting their properties to different environments. Fabrics containing catalytic molecules will be able to break down toxic chemicals without requiring bulky, impractical suits. And maybe, optical camouflage will become reality...

1 Ultra-High Molecular Weight Polyethylene: very long polymeric chains with better mechanical properties than shorter ones.

2 Poly(TetraFluoroEthylene): a polymer (known also with the trade name of Teflon) with extreme chemical stability. Almost nothing can stick to PTFE.


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