إِلَّا جِلْدَ الْخِنْزِيرِ وَالْآدَمِيِّ
Translation: Except the skin of the pig and the human being.
Pig skin is not purified by tanning because its impurity is not treated as merely the decaying moisture within the hide.
Human skin is excluded on grounds of human dignity: treating it for use as a material is impermissible. The rationale of human sanctity must not be confused with that of pig skin.