According to Genesis, Noah coated the ark inside and outside with pitch.
Genesis 6:14 tells Noah to cover the vessel with pitch, using the same instruction for its interior and exterior surfaces. Pitch is a thick, waterproofing substance traditionally made from natural bitumen, wood tar, or related materials. In the story, it helps explain how the large vessel was sealed against water.
The Hebrew wording is related to terms for covering or atonement, and translations differ in how they render the substance. “Pitch” is the standard English answer in many Bible translations, while some versions use “bitumen” or “tar.” These terms describe waterproofing material, not a separate structural wood.
The instruction is distinct from the ark’s building material, which Genesis calls gopher wood. One describes what the ark was made from; the other describes how it was sealed.