Ancient codexes were typically written on vellum, which is a sheep-skin stretched thin and sewn together. Thus they were extremely expensive.
The word papyrus /pəˈpaɪrəs/ refers to a thick type of paper made from the pith of the papyrus plant, Cyperus papyrus.[1] Papyrus can also refer to a document written on sheets of papyrus joined together side by side and rolled up into a scroll, an early form of a book. The plural for such documents is papyri.
An official letter on a papyrus of the 3rd century BC Papyrus is first known to have been used in ancient Egypt (at least as far back as the First Dynasty), as the Cyperus papyrus plant was a wetland sedge that was once abundant in the Sudd of Southern Sudan along with the Nile Delta of Egypt. Papyrus was also used throughout the Mediterranean region and in Kingdom of Kush. The Ancient Egyptians used papyrus as a writing material,[2] as well as employing it commonly in the construction of other artifacts such as reed boats, mats, rope, sandals, and baskets.
https://en.m.wikipedia.org/wiki/Papyrus
Technically speaking, the term "vellum" is strictly for cow/calf skin. Parchment is the proper term for goat, sheep or other skins.