The general rule establishes purification of hides through tanning and thereby permits ordinary uses such as garments or leather water containers. Pig skin and human skin are excluded, but for distinct legal reasons.
Carrion hair and bones are governed by a separate Hanafi principle, with Shafi‘i and Maliki disagreements. The details also involve physical versus constructive tanning, dog and elephant hides and contact with impure tissue at hair roots.
The next topic is impurity falling into a well.