Keilim 27:2-3

Keilim 27:2

Cloth is susceptible to midras impurity when it’s three handbreadths by three handbreadths, and to corpse impurity when it’s three fingerbreadths by three fingerbreadths. Sackcloth is susceptible when it’s four handbreadths by four handbreadths, leather when it’s five handbreadths by five handbreadths, a mat when it’s six handbreadths by six handbreadths. These latter measures are the same for both midras and corpse impurity. Rabbi Meir says that a remnant of sackcloth is susceptible to impurity when it’s four handbreadths but it only becomes susceptible initially once its manufacture has been completed.

Keilim 27:3

If something is made of two handbreadths of cloth and one of sack, or three of sack and one of leather, or four of leather and one of mat, it is insusceptible to impurity. If it’s made of five handbreadths of mat and one of leather, or four of leather and one of sack, or three of sack and one of cloth, it is susceptible. The general principle is that if the additional part is more stringent, the combination is susceptible to impurity; if the addition is more lenient, the combination is insusceptible.