In Halacha, is there a requirement for the straps made for tefillin to be made out of animal skin such as leather, or no? If there is a requirement, is it Derabbanan, or a Halacha LeMoshe Misinai? Or is it derived from Drash in the tanakh?
The straps must be made of skins of a kosher animal (OC 33:3, cf. Shabbat 28b).
Pri Megadim is unsure if this requirement is biblical (like by the other components of tefillin) or only rabbinic.