Kelim, Chapter Twenty-Four, Mishnah Sixteen
There are three different types of hair nets:
1) A girl’s is susceptible to midras uncleanness;
2) An old woman’s is susceptible to corpse uncleanness;
3) And [the hair net] of a woman who “goes out” is free from all uncleanness.
Section one: A girl’s hair net is made so that it can also be sat upon. Therefore, it is susceptible to midras.
Section two: According to our mishnah, an old woman’s hair net is not made to be sat upon, therefore it is not susceptible to midras. Note that in 28:9 the Mishnah will teach the opposite: a girl’s is susceptible only to corpse uncleanness but an old woman’s is susceptible to midras. Albeck seems to think that the version preserved in 28:9 is more accurate.
Section three: There are two explanations for a woman who “goes out.” Some explain this to be a temporary hair net used by a woman who merely goes out to the courtyard. Others explain that a woman who “goes out” refers to a prostitute. Her hair net does not cover much hair so it is not considered a vessel.