Parchment is a material made from processed animal skin and used—mainly in the past—for writing on. Parchment is most commonly made of calfskin, sheepskin, or goatskin. It was historically used for writing documents, notes, or the pages of a book. Parchment is limed, scraped and dried under tension. It is not tanned, and is thus different from leather. This makes it more suitable for writing on, but leaves it very reactive to changes in relative humidity and makes it revert to rawhide if overly wet.