For those who like to make their workpieces entirely from natural materials, including the filling, there is this washed and carded wool from South German merino sheep. For dolls, pillows, felted cobblestones and other applications where you need volume.
The wool has a fairly short fiber and is pretty resilient. Because it is carded, you can fill it nicely regularly, so without unwanted thickening and empty spots. This is also a suitable wool for needle felting larger (basic) shapes.