An IOU is a written document indicating the relationship between creditor's rights and debts, which is generally written and signed by the debtor, indicating that the debtor has owed the creditor the amount indicated in the IOU.
There is no strict requirement for paper. Please use good quality paper for long-term storage. If possible, try to write with black ink pen, as long as the handwriting is clear. When selecting paper, you must pay attention to the following points:
First, paper is easy to write, that is, it won't scratch and spread when writing;
Second, try to choose blank paper to avoid confusion between the existing handwriting or printed words and the contents of the loan;
Third, try to choose paper that has been preserved for a long time to avoid oxidative damage for a long time.