Fibre fineness is measured in micrometres of diameter, and the difference between grades is small in absolute terms and enormous in feel. Fine merino sits in the high teens, good cashmere in the mid teens, and vicuna at roughly twelve.
The yield is tiny. A vicuna carries only a few hundred grams of usable fleece and is shorn no more than once every two years, which is why finished cloth is among the most expensive textiles sold. Under the Inca state, animals were rounded up in a communal drive called the chaccu, shorn and released, and the cloth was restricted to the ruling class.
Hunting for that fleece nearly finished the species, which fell to a few thousand animals by the 1960s before protection and community-managed chaccu brought it back to the hundreds of thousands. Poaching continues, and how reliably the revenue reaches the Andean communities doing the herding is disputed rather than resolved.