"The plates are made of paper."
Translation:La teleroj estas el papero.
I really expected "de" to work here, although "el" seems natural too. "de" seems often to be used in conjunction with far/i to describe the composition of something, so I reckoned it would also work with est/i.
El is the preposition used to express what something is made of: tablo el ligno (wooden table), glaso el plasto (plastic glass), poto el metalo (metal pot).