Borrowed from Wools of New Zealand:
Wool production compares favourably with the manufacture of man-made fibers in regard to energy consumption, as expressed in tonnes oil equivalent per tonnes fiber produced. In fact, wool only uses between one-third and one-sixth of the energy required to produce polypropylene or nylon fibers. And there’s more good news – wool’s superior heat insulating properties save on heating costs.
Energy consumption per kg of fiber (MJ/kg) based on a life cycle analysis of carpeting by Utrecht University in the Netherlands is as follows: