Actually, not all skull caps can be redistributed with hair.  PhilC does have some skull caps that you can use to grow hair and destribute the hair though. 

A skull cap just allows you to grow your own hair and save it as a prop in your library for future use.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi