Keilim, Chapter 28, Mishnah 4. The subject here is the cloth cover used for a Sefer Torah. It is a flat piece of material, not a receptacle of any kind, and it was wound around the scroll. To understand the dispute in this mishnah, we need one principle: a flat utensil that exists to serve another object, and does not give service to a person directly, is not susceptible to tumah at all. The question our mishnah records is whether the cover of a Sefer Torah falls into that category, and here Beit Shammai, Beit Hillel and Rabban Gamliel each take a different position.
The mishnah's first words are "Mitpechot sefarim", the wrappings in which scrolls are kept. Concerning these, Beit Shammai rule that they can contract tumah, "bein metzuyarot", whether designs have been worked into them, "bein she'einan metzuyarot", or whether they are entirely plain, and the mishnah records their position as "temei'ot, kedivrei Beit Shammai". What stands behind this ruling is that in practice such a wrapping does render a service to the person handling it. Imagine a man in the middle of his learning who is called away: he places the wrapping at the spot he had reached, so that upon returning he can pick up precisely where he stopped. For Beit Shammai, a use of that sort stamps the cloth as something a person employs for his own needs, and whatever is employed for a person's needs is included among the utensils that can become tamei.
Beit Hillel divide the cases: "metzuyarot tehorot, veshe'einan metzuyarot temei'ot". A cover that is decorated remains tahor, since a decorated cover is clearly there for one purpose alone, to cover the scroll, and not to give any service to a person. The very fact that it was embroidered and adorned tells us how it is regarded: nobody would take such a piece and use it as a place marker in his learning. When a person spreads it over the Sefer Torah he is acting out of honor for the scroll, not for any need of his own. But an undecorated cover, says Beit Hillel, is susceptible to tumah, because a plain cloth is put to additional uses as well, uses that do serve the person handling it, and that is what gives it the capacity to receive tumah.
The third and final view is that of Rabban Gamliel: "elu va'elu tehorot". Both kinds of cover, the decorated and the undecorated alike, remain tahor. In his understanding the essential function of any such cover is to cover the scroll, and once that is its defining role, people are not likely to press it into other uses even when it carries no decoration. Since it therefore does not serve a person, it never enters the category of a utensil that can become tamei.
So this short mishnah gives us three readings of one simple cloth. Beit Shammai look at how it is actually handled in the study hall and call it an article of human use in every case; Beit Hillel let the decoration itself testify to the cloth's purpose and distinguish accordingly; and Rabban Gamliel fixes the cover's identity by its primary function, service of the Sefer Torah, and rules that it stays tahor across the board.