The technique presented in this recipe is known as Lengyel's concentric fur-shell technique or simply the shell technique. It works by creating progressively bigger copies of the geometry that needs to be rendered. With the right transparency, it gives the illusion of a continuous thread of hair:
The shell technique is extremely versatile and relatively easy to implement. Realistic fur requires not only extruding the geometry of the model but also altering its vertices. This is possible with tessellation shaders, which are much more advanced and not covered in this book.
Each pass in this Fur Shader is contained in FurPass.cginc ...
