On what kind of paper did Paul write his letters on?

Paul likely wrote his letters on papyrus, a common writing material in the ancient Mediterranean world. Papyrus sheets were made from the pith of the papyrus plant and were used for scrolls and letters. In some cases, he may have also written on parchment, which is made from animal skins and was used for more durable documents. The specific choice of material would have depended on availability and the intended use of the letters.