'Kolinsky'  is a market name of the hair used for brush making. It's the best raw material to produce second to none art brushes for watercolour painting  and for finest details and  line work with oils and acrylics. 

The hair comes from an animal belonging to the subfamily Mustelinae (weasels, sables, ferrets, minks,etc.). 
Genetically, a Mustela sibirica is close to a European mink. A scientific name of the animal is Mustela sibirica or Siberian weasel or Siberian Kolinsky or 'kolonok'. This means, that the so-called 'Kolinsky Sable', 'Pure Red Sable' or 'Red Sable' brushes are made from weasel hair, not sable hair! The animal used to populate the Kola Peninsula ('Kol-insky') but does not inhabit this area anymore. Its hair has hues from light yellow to dark brown  with darker tips.  In summer kolonok's fur is darker than in winter. The most expensive quality brushes are produced from  winter tails of  male Siberian weasels. One gram of top quality Kolinsky hair is worth more than its weight in gold. Brushes jump up in value dramatically if of top quality. It's also true that the round brushes that are bigger than size 14 ( 14 mm in diameter) are rare.

From http://www.ferret.ru/page-129

Because of its unique characteristics the Siberian weasel tail fur makes the finest watercolour and oil paint brushes that are especially sought after by artists.  The brush keeps a superfine point, has smooth handling and good memory  as it springs back to its original state. The tips are very fine and the resilience is better than of squirrel hair.  The maximum thickness of a spindle-like hair is 0.15mm in the middle what can be compared with the thickness of a hog bristle and a tip is very fine like squirrel's one.

The closest to Siberian Kolinsky hair by quality is so-called 'Red Sable' or 'Pure Red Sable' hair from Korea and China but it is softer and more brittle. The severe winters the better the fur of animals. The Korean and Chinese 'Red Sable' hair has a longer rachis but the difference in the thickness along the hair up to the tip is not so strongly pronounced. If it's treated well this kind of hair becomes hard to distinguish from Siberian Kolinsky.

You have an opportunity to buy real Siberian Kolinsky brushes which guarantees the highest quality required and expected!