Years ago, when I was a schoolboy, I used this paint brush with natural hair looking bristles. It is from an Indian brand named Camlin. But these types of brushes are no longer available in the market even from the same brand. Does any one know what is the hair used (pic attached) and which brand has this still in production.
My guess is that it's badger hair - the grey-white gradations are typical for these kinds of brushes:
They are quite common, and many manufacturers produce them, including Da Vinci, Isabey, Royal & Langnickel, and Raphael.
Unlike other hair, pure badger hair is thickest at the tips, giving these brushes a bushy appearance. They're excellent for glazing techniques, and popular with decorative and faux finish painters because of their blending ability. source
Badger brushes are [..] more springy than bristle, and they have a softer touch. They cost more but seem to last forever (I have some which are twelve years and counting). source