In the Epic of Gilgamesh, bitumen was used to waterproof the flood vessel.
In the flood story told by Utnapishtim, the boat is coated with bitumen, a naturally occurring petroleum-based material used in the ancient Near East as a sealant. Waterproofing with bitumen was practical for boats and buildings because the thick substance could fill gaps and resist water.
This detail belongs to the Mesopotamian literary tradition, not to the exact wording of Genesis. Genesis says that Noah covered the ark with pitch, a related waterproofing idea, but the two narratives use different languages, measurements, and vessel descriptions.
The technical detail helps show that ancient flood stories were rooted in the construction practices of their region. It also explains why translations may use terms such as bitumen, pitch, or asphalt for comparable materials.