For ages, the Merino sheep has been prized for its fleece which is the finest and softest over any other wool, so much so that before 18th century Spain only the nobility and the church owned most of the flocks and that export of these was punishable by death. After the Napoleonic Wars, the breed has spread to Germany, the United States, Australia, and New Zealand.
The Merino wool is noted for its excellence at regulating body temperatures and though it absorbs water, it retains its warmth when wet making it ideal for athletic clothing. Unlike synthetic fabrics, the Merino is superior in that its fibers biodegrade rapidly according to New Zealand researchers. When completely buried in soil for intervals of 1, 2, 3, 6, and 9 months, merino samples lost 36% of their mass at two months and 76-99% at nine months. Compared to its synthetic counterpart, which did not degrade when buried after nine months, merino has a superior advantage of being sustainable and eco-friendly.
Source: http://www.knittingindustry.com/articles/1691.php, http://en.wikipedia.org/wiki/Merino