United States paper money can be taken to a bank and exchanged for currency in good condition as long as it is not mutilated. Mutilated currency needs to be examined by experts at the Bureau of Engraving and Printing.
The U.S. Bureau of Engraving and Printing explains various ways currency can be damaged. Money that is heavily damaged, such as by water or fire, is considered to be mutilated. Most worn currency is classified as nonmutilated; this classification applies to torn or dirty banknotes. When more than half of the original banknote is present and no special effort is required to determine the face value of the bill, it is easy to exchange the note for a replacement at a local bank.