According to Genesis, Noah’s Ark was covered with pitch.
Genesis 6:14 tells Noah to cover the ark inside and outside with pitch after building it from gopher wood. Pitch is a waterproofing substance derived from tar-like or resinous materials, and its stated purpose was to seal the vessel against water.
The Hebrew wording is related to the idea of covering or atoning, which has encouraged linguistic discussion, but the practical narrative function is clear: the ark needed a waterproof coating. Genesis does not specify the exact chemical recipe, source, or application method.
Some retellings say the ark was sealed with tar, bitumen, or resin. These terms can describe related waterproofing substances, but “pitch” is the traditional English answer that follows the wording of many Bible translations. The text says the coating was applied both inside and outside, not merely to the exterior.