A woman may sit and set aside her challah while naked, because she is able to cover herself; but not a man.  [If] one is unable to make his dough in [a state of] taharah —- he should make it kav portions, but should not make it in tumah. But R' Akiva says: He should make it in tumah, but should not make it kav portions; for just as one designates [challah] for a tahor [dough], so he designates [challah] for a tamei [dough] —- he assigns the designation “challah” to [a portion of] this [tahor dough] and he assigns the designation “challah” to [a portion of] this [tamei dough]; but kav portions have no share in the designation [“challah”].