Mine, pictured above, is made from horse tail hair from 2 of our horses. I started with about 50 hairs that were about 5" long. I would suggest fewer hairs, maybe as few as 10 hairs.
I first tied the hairs in a loose knot, then began rolling between my hands.
Once these were well bound together in a small ball I added a considerably smaller grouping of hairs.
I tucked them into the ball a bit, then began rolling.
This gathering of a group of hairs and rolling continued until the ball was the size and density I was happy with.
The entire process took less than 10 minutes. Making them for others is simple and quick.