Book weights typically come under the name of weighted bookmarks. Personally, I never liked the idea of using anything but a flat paper or thin plastic bookmark, because other types of bookmarks can damage the book. The purpose of book weights is to hold down the book’s pages so they don’t close. Book weight is a great way to deal with a major inconvenience (especially if you are taking notes) without having to use bulky book holding devices. Leather is a common material for weighted bookmarks. I have seen some made out of wood or metal, but delicate book pages can be easily damaged by sharp edges of such bookmarks.