In Genesis, Noah used pitch to cover the Ark and make it watertight.
Genesis 6:14 instructs Noah to coat the Ark inside and outside with pitch. The Hebrew word is related to bitumen or a waterproofing substance, although translations differ in how they render the term. “Pitch” is the conventional English answer because it matches the wording of many major Bible translations.
The instruction is practical within the story: the Ark is described as a large vessel with compartments, and the coating would seal its wooden structure against water. Genesis gives the waterproofing instruction alongside the choice of gopher wood.
Pitch should not be confused with the Ark’s material. Gopher wood identifies the building material in the narrative, while pitch describes the protective coating. The text does not specify a modern chemical formula or explain how the substance was processed.