Kelim, Chapter Twenty-Six, Mishnah Six
1) A bag or wrapper for garments is susceptible to midras.
2) A bag or wrapper for purple wool:
a) Bet Shammai says: it is susceptible to midras,
b) But Bet Hillel says: it is susceptible only to corpse uncleanness.
3) A hide which was made to be a covering for vessels is not susceptible to uncleanness, but for weights it is susceptible.
a) Rabbi Yose says in the name of his father that it is pure.
Section one: Since these leather bags or wrappers are occasionally sat upon, they are susceptible to midras.
Section two: Purple wool was more expensive than regular cloth. Due to its expense, Bet Hillel holds that one would not use a bag or wrapper of purple wool for sitting or lying upon. Bet Shammai disagrees and does not differentiate between wrappers and bags for regular clothing and wrappers or bags for purple wool.
Section three: A hide that is simply used as a covering for regular vessels does not have a receptacle and therefore is free from impurity. However, a hide used as a covering for weights used on scales does have a receptacle, so it is not susceptible to impurity.
Rabbi Yose states in the name of his father, R. Halafta, that even hides used to cover weights are not susceptible to impurity.