Kelim, Chapter Twenty-Four, Mishnah Eight
There are three different types of beds:
1) One that is used for lying upon is susceptible to midras uncleanness;
2) One used by glass makers is susceptible to corpse uncleanness;
3) And one used by weavers is free from all uncleanness.
Section one: A regular bed made to lie upon is susceptible to midras uncleanness.
Section two: Glass makers would use the bed to arrange the glass that they had already made. This type of bed is considered a vessel and therefore is susceptible to impurity. I should note that some of the commentators ask why this type of bed is considered to be a vessel and is susceptible, whereas the wagon used in olive making (mishnah five) is pure. The same question might be asked concerning the next section: why is this bed susceptible but a bed used by weavers not?
Section three: The bed used by weavers (there are various interpretations as to how this bed is used) is pure because it is not considered to be something used by a person.