"Why Does a Vicuña Jacket Cost $21,000?"

If you're perfectly happy with fine cashmere, all this might seem like a lot of trouble to go through for an extra layer of luxury. But come into contact with vicuña and you might, for a moment, think seriously about blowing your children's college funds.

Vicuña coats and jackets have an unparalleled lightness that makes you feel almost buoyant. And then there is the softness. "People love vicuña for the touch," said Mr. Loro Piana. "It's the finest hair on the planet." The diameter of its fiber is 12.5 microns, he explained, while the best cashmere is 13.5 microns and run-of-the-mill cashmere ranges from 14.5 to 17.5.

Incan royalty wore it exclusively. In the 1500s, King Philip II of Spain slept under vicuña blankets. Last century, it was favored by wealthy entertainers: Greta Garbo wore vicuña, as did Nat King Cole and Marlene Dietrich.

Each year, only 13,000 to 17,500 pounds of vicuña become available to Loro Piana, a major purveyor of vicuña garments—a fraction of the 22 million pounds of cashmere the company works with annually. The Italian tailoring house Kiton makes only about 100 vicuña pieces a year; an off-the-rack sport coat costs at least $21,000, while the price of a made-to-measure suit starts at $40,000. A single vicuña scarf from Loro Piana is about $4,000. Ermenegildo Zegna produces just 30 vicuña suits a year. Each is numbered, and the most affordable model goes for $46,500.

The vicuña, a camelid that looks like a smaller and more elegant llama, is found primarily in the Peruvian and northern Argentine Andes. For centuries, it was poached for its valuable cinnamon-colored coat, a marvel of evolution that, although unusually light and fine, keeps the animals warm in the freezing altitudes above 15,000 feet. By the 1960s, the vicuña population had fallen from an estimated two million in the 16th century to roughly 10,000, and Peru took measures to protect vicuñas from extinction, banning the killing and trade of the animals.

Learn more about vicuña and the vicuña here.