Keilim 27:12

Let’s say that a piece of cloth three handbreadths by three handbreadths got torn. If one puts it on a chair and his skin touches the chair through the rip, then the cloth is insusceptible to midras, otherwise it remains susceptible. If one thread of a cloth three fingerbreadths by three fingerbreadths was worn away, a knot was found in it, or two threads ran together, the cloth is insusceptible to impurity. A cloth three fingerbreadths by three fingerbreadths on a trash heap is insusceptible to impurity; if one takes it back, it reverts to susceptibility. Throwing such a cloth away always purifies it and taking it back returns it to susceptibility except in the case of purple and fine crimson cloth; Rabbi Eliezer also includes a piece of new cloth. Rabbi Shimon says that all of these are purified when thrown away; they were only mentioned vis-à-vis the obligation to return them as lost property.

Keilim 28:1

If a cloth three fingerbreadths by three fingerbreadths was stuffed into a ball or made into a ball, it is insusceptible to impurity. If a cloth three handbreadths by three handbreadths was stuffed into a ball, it remains susceptible to impurity but if he made it into a ball, it is insusceptible because sewing it reduces it in size.