Genesis says Noah covered the Ark with pitch inside and outside.
The instruction appears in Genesis 6:14. Pitch is a waterproofing substance made from tarry or resinous material, and ancient boat builders used related substances to seal wooden hulls and prevent water from entering. The Hebrew wording uses a term related to covering or atonement, while the practical image is of a protective coating.
The passage pairs this coating with the Ark’s wooden construction and internal rooms. Together, the details present the vessel as a sealed wooden structure rather than as a conventional open-deck boat. Genesis does not identify the exact chemical composition of the pitch or describe how often the coating was reapplied.
Some readers answer “bitumen,” which is a reasonable technical gloss for an ancient waterproofing material, but the standard English wording of the Genesis instruction is “pitch.” The question therefore uses that canonical term.