QOUTE WIKIPEDIA:
"Characteristics
Wool's scaling and crimp make it easier to spin the fleece. They help the individual fibers attach to each other so that they stay together.
Because of the crimp, wool fabrics have a greater bulk than other textiles and retain air, which causes the product to retain heat. Insulation also works both ways; Bedouins and Tuaregs use wool clothes to keep the heat out.
The amount of crimp corresponds to the thickness of the wool fibers. A fine wool like Merino may have up to a hundred crimps per inch, while the coarser wools like karakul may have as few as one to two crimps per inch. Hair, by contrast, has little if any scale and no crimp, and little ability to bind into yarn. On sheep, the hair part of the fleece is called kemp. The relative amounts of kemp to wool vary from breed to breed, and make some fleeces more desirable for spinning, felting, or carding into batts for quilts or other insulating products.
Wool possesses much greater ability to return to its natural length after being stretched than any artificial fiber. In water or steam, wool can stretch to about twice its length without breaking. Because of elasticity, woollen garments may be stretched or crushed without losing their shape. Also, this fiber felts readily, by heat, moisture, and pressure being applied during the manufacturing processes.
Wool fibers are hygroscopic. This means wool has the power to readily absorb and give off moisture. It can absorb moisture up to one-third of its own weight. Synthetic fibers can only absorb 2-3 percent of moisture before they begin to feel wet. Additionally, wool absorbs sound and reduces noise level considerably like many other fabrics. Wool is generally a creamy white color, although some breeds of sheep produce natural colors such as black, brown, silver, and random mixes.
Wool is harder to ignite than most synthetic and cotton fibers used in equivalent products (higher ignition temperature); it has lower rate of flame spread, low heat release, and low heat of combustion; doesn't melt or drip; forms a char which is insulating and self-extinguishes; and contributes less to toxic gases and smoke than other flooring products when used in carpets. Wool carpets are specified for high safety environments such as trains and aircraft. Wool is usually specified for garments for fire-fighters, soldiers, and others in occupations where they are exposed to the likelihood of fire.[3]
Wool is static resistant as the retention of moisture within the fabric prevents a build up of static electricity. Woollen garments are much less likely to spark or cling to the body. The use of woollen car seat covers or carpets reduces the risk of a shock when a person touches a grounded object."
more from a physics discussion forum:
http://www.physicsforums.com/showthread.php?t=270141
more info:
http://www.straightdope.com/columns/read/108/how-does-wool-keep-you-warm-when-its-wet
" Each wool fiber (measuring about a thousandth of an inch in diameter, depending on the grade) consists of a bundle of corticle cells, made up of polypeptide chains arranged in coils. These corticle cells are wrapped up in a scaly outer layer called a cuticle, which in turn is covered by a filmy skin called an epicuticle. The epicuticle actually sheds drops of water.
In addition, raindrops are less likely to break up on the surface of wool and seep through than with other fabrics, since the fuzziness of the fibers cushions the fall. So in a light rain, much of the water runs right off, the fabric hardly getting damp at all.
But the real genius of the wool fiber lies in its ability to cope with the high humidity that you may get during rainstorms or at other times. The sheep (they may look stupid, but it's all an act) have cleverly equipped the epicuticle with tiny pores that allow water vapor to pass through to the core, where it's chemically absorbed. A single fibre can slurp up to 30 percent of its own weight in moisture without feeling wet.
Wool does act as a natural insulator, thanks to its built-in crimp.
The fibers repel each other, keeping a bit of dead air in between them. But
it's the epicuticle that does the heavy lifting when it comes to keeping you warm despite the wet.
— Cecil Adams"
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and all this science aside, the proof for me that wool is warmer when wet is the approx 1000+ times i have ventured into the woods here, the RAINFORESTS of BC Canada, where rain can and WILL kill you, all those times i have been WARM in wool, and the times i have worn only fleece, i have been COLD and hypothermic. Out here that will kill you within hours. Wool has kept me alive all my life in these woods. Andf that for me is proof enough
YMMV
