1) Insulation: Wool fabrics, and especially felt, have a greater bulk than other textiles because of the crimp, and retain air, which is a great insulation. It keeps your body heat in when the surrounding environment is cold, but insulation also works both ways; if the air is hotter than your body temperature, a wool layer not touching the skin will keep the heat out.
2) Ecological: Wool fiber requires no factory to produce it. Part of its own miracle is that it is self replenishing. Its source, the sheep, llamas, goats, etc. live for many years, fed by vegetation, which is also self-replenishing.
3) Protein Fiber: Wool is made of keratin, a protein fiber that is tougher and more durable than the cellulose of cotton fibers and the like. It has more tensile strength per thickness of fiber, it is nearly impervious to rot and mildew, and it does not harbor odor-causing bacteria after prolonged wear without wash.
4) Fire: Wool doesn’t ignite. A loose protein fiber will get denatured (in the form of shriveling and disintegrating) when in direct contact with flame, but will not in catch fire. Campfire embers will not burn a hole in wool. Wool will not melt on to the skin, like many common synthetics
5) Compostable: In this era of mounting concern about what to do with discarded products no longer of use to anybody, the compostable quality of wool, as opposed to petroleum synthetic, is more important then ever. A woolen garment can endure heavy use for years and when it finally gives out it can be returned to the earth for natural recycling.
6) Electricity: Wool is resistant to static electricity, because the moisture retained within the fabric conducts electricity. This is why wool garments are much less likely to spark or cling to the body. The use of wool car seat covers or carpets reduces the risk of a shock when a person touches a grounded object.
7) Water resistant: Wool felt is highly water-resistant. While felt can be made to absorb water by submerging and wringing, falling raindrops and snowflakes get caught in the fuzz and can be brushed off. Wool absorbs a high volume of moisture, so prevents the body from getting chilled by damp air, and also wicks sweat from the skin. This makes it breathable and extremely comfortable next to the skin. It prevents the clammy, cold feeling you may experience when wearing some types of synthetic clothing and sweating.
8) Durability: Wool fibers can be bent 20,000 times without breaking (compared to cotton, which breaks after 3,000 bends or rayon, which can be bent only 75 times without breaking), and have the power to elongate (it can be stretched 25 – 30% before breaking), stretch and recover. This natural elasticity and memory returns to its natural shape
Above information used with permission from http://feltthesun.com/why_wool