What paper was the cover of ancient books made of?

Initially, it was used to bind and protect the inside pages. Perhaps the earliest form is package-based. If the contents of the bag don't need to be changed frequently, the inside pages are fixed in the book cover with rope or glue. /kloc-in the 0/9th century, people used boards, leather, gold and silver as book covers, because books were expensive at that time. With the development of technology, the price of books dropped, and wooden boards were used.