Genesis says Noah coated the Ark with pitch.
Genesis 6:14 instructs Noah to make the ark from gopher wood and to cover it inside and outside with pitch. Pitch is a waterproofing substance, commonly understood as a bituminous or resinous material. The coating would help seal the wooden structure against water.
The Hebrew wording is related to the root for covering or atonement, and translations vary in how they render the substance. English versions commonly use “pitch,” while some descriptions discuss bitumen, tar-like material, or an unspecified waterproof coating. “Pitch” is therefore the standard concise answer to the biblical wording.
The text gives no modern chemical formula and does not describe an industrial manufacturing process. It presents pitch as part of the ark's construction instructions, alongside its compartments, door, and upper opening. Similar waterproofing materials were known in the ancient Near East for boats, containers, and building work, making the detail consistent with the practical setting of the narrative.