A board book is a type of book printed on thick paperboard. The paperboard is printed and used for both the cover and the interior pages. Each page panel is a minimum of two plies of paperboard thickness. Unlike a typical paper book that is bound with saddle stitching (staples) or perfect binding, a board book's pages are specially folded and bound together. Board books are very durable and consequently intended for small children as they often tend to be destructive and unpredictable. Many best-selling titles that were originally published in hardcover or paperboard formats have been converted to board books.