I thought it would be useful to know and understand the types of cover materials that are used. In the 5th Century books were first bound with hard covers. The pages were made with parchment and the covers were bound on wood with leather covers over the top.
The St Cuthbert Gospel is the oldest known book with a surviving bookbinding. The 7th Century book is written in fine Latin with beautiful decorated manuscripts across the page. The covers are also finely decorated, made of red goatskin. The front cover is a pigment filling that is engraved in what appears to be shades of yellow.
The back cover is quite different. There are no pigments raised on the back, and there are only details of engraving similar to the front. Both of the sides are equally beautifully detailed and centered on the book. In the 15th Century, the Gold leaf was imported from the Islamic World, which were then used for bindings on luxury books.
Today, book cover materials come in a variety:
Pearl Linen B
80# Paper Cover