Kelim, Chapter Twenty-Seven, Mishnah Two
1) Cloth is susceptible to midras uncleanness when it is three handbreadths by three handbreadths, and to corpse uncleanness when it is three fingerbreadths by three fingerbreadths.
a) Sack-cloth when it is four handbreadths by four handbreadths.
b) Leather, five handbreadths by five handbreadths.
c) And matting, six handbreadths by six handbreadths.
i) [All of these] are equally susceptible to both midras and corpse uncleanness.
2) Rabbi Meir says: what remains of sack-cloth is susceptible to uncleanness if it is four handbreadths, but when in its first condition [it becomes susceptible only after its manufacture] is completed.
Section one: This section provides minimum sizes for various materials to be susceptible to impurity. When it comes to cloth, there is a distinction between the minimum size susceptible to midras impurity and corpse impurity. For a piece of cloth to be susceptible to midras, it must be a piece of cloth that someone might use for sitting on or laying upon. Thus it must be at least three by three handbreadths. But for it to be susceptible to corpse impurity it need be only three by three fingerbreadths, which is quite a small piece of cloth. We can learn from here of the value of cloth during the mishnaic periodpeople would save pieces as small as one’s fist.
When it comes to the other materials, there is no distinction between the minimum size to be susceptible to midras or corpse impurity.
We should also note that the mishnah demonstrates the relative value of materials. Cloth was most valuable, then the coarser sack-cloth, then leather and finally matting, which was made from reeds.
Section two: Rabbi Meir partially modifies the halakhah found in section one. Sack-cloth that remains from a larger piece of sack-cloth is impure as long as four handbreadths by four handbreadths remain. This accords with the previous opinion. However, when one first manufactures a piece of sack-cloth, it is not susceptible to impurity until it is finished. If it is unfinished, it is not susceptible, even if it is larger than four by four handbreadths.