What is "gevil"

Gevil or Gewil is animal hide that has been prepared as a writing material in Jewish scribal documents, in particular a Sefer Torah (Torah scroll).

According to most views of Jewish Law, a sefer Torah (scroll) should be written on gevil as was done by Moses for the original Torah scroll he transcribed. Further, a reading of the earliest extant manuscripts of the Mishneh Torah indicate that gevil was halakha derived from Moses and thus required for Torah scrolls.

Maimonides wrote that it is the law transmitted to Moses on Mount Sinai that a Torah scroll must be written on gevil or alternatively on klaf and that scrolls written on an alternative material are invalid for use, however it is preferable that they be written on gevil (Maimonides, Hilkhoth Tefillin 1:14).