The material typically used for the pages was parchment, which is animal skin that's stretched and dried under tension, so it become s really flat and can be written on.

书页通常使用的材料是羊皮纸，羊皮纸是一种动物的皮肤，其在张力的作用下被拉伸和变干，因此它会变得非常平整，并且你可以在上面写字。

youdao

The Dead Sea commandments were written in Hebrew on parchment made of animal skin.

FORBES: Ancient Ten Commandments Manuscript On Display