Noah was told to use pitch to make the Ark watertight.
Genesis 6:14 instructs him to make the ark from gopher wood and cover it with pitch inside and out. Pitch is a waterproofing substance, generally understood as a tar-like or resinous coating. The verse’s wording emphasizes that the coating was applied to both the interior and exterior surfaces.
The exact identity of “gopher wood” is uncertain. The Hebrew expression occurs only in this passage, so scholars cannot identify its tree species with confidence. Pitch, by contrast, is clear as a waterproofing material even though ancient methods and ingredients may have varied.
Some retellings replace pitch with bitumen, tar, resin, or wax. These terms can overlap in broad descriptions of ancient waterproofing, but “pitch” is the conventional English answer to the Genesis wording. The text gives no detailed construction recipe, measurements for the coating, or account of how the material was manufactured.