Kolinsky sable is a type of animal hair used in top-quality artist's brushes for watercolor, oil, and ink-brush painting. Despite the name, the hair doesn't come from a sable, but from a Siberian weasel (Mustela sibirica). The hair is dark red along its length, turning black at the tip.
Kolinsky sable brushes are prized for the way they hold paint, the sharp point (which is retained when wet), the spring or bounce in the hair as you use it. The most expensive Kolinsky sable brushes are made using hairs of varying lengths to give a very fine point. If cared for properly, a Kolinksy sable brush will give many years of use.