A hardcover (or hardback or hardbound) is a book bound with rigid protective covers (typically of cardboard covered with cloth, heavy paper, or sometimes leather). They may have flexible sewn spines which allow the book to lie flat on a surface when opened, although most modern commercial hardcover books have glued spines. Hardcover books are often printed on acid-free paper, and are much more durable than paperbacks, which have flexible, easily damaged paper covers and glued spines. Hardcover books are also marginally more expensive to manufacture and usually much more to purchase. Hardcovers frequently come with artistic dust jackets.