Paintbrush hairs

What are the little hairs, or “bristles” as they are known, on a paintbrush made from?

Edit: Wow - I don’t know what I’ve been doing wrong before, because I could never find an answer, though a Google search reveals this on the first hit: Know Your Painting Brush Hairs and Bristles. Silly me.

There is no one answer to this. It depends on the paint brush. Some are synthetic and others are not. Natural ones might be made of boar bristle, sable, etc.

Edit to add:

You found the same article I did. For some reason I was never able to find an answer before, until just after I asked the question.