Kayan yumbu yana nufin kayan da ba na ƙarfe ba waɗanda ba na halitta ba ne waɗanda aka yi da mahaɗan halitta ko na roba ta hanyar samarwa da kuma yin sintering. Yana da fa'idodin wurin narkewa mai yawa, tauri mai yawa, juriya mai yawa da juriya ga iskar shaka. Ana amfani da hatimin injina na yumbu sosai a cikin injina, masana'antar sinadarai, man fetur, magunguna, motoci da sauran fannoni.
Hatimin injina suna da babban buƙata game da kayan rufewa, don haka ana ɗaukar yumbu don yin hatimin injina na yumbu saboda fasalulluka masu gasa.
