Noah was told to coat the Ark inside and outside with pitch.
Genesis 6:14 says Noah should make the Ark from gopher wood and “cover it inside and outside with pitch.” The coating would have served as a sealant, helping make the wooden structure resistant to water. The Hebrew word used in the passage is related to terms for bitumen or a waterproofing substance.
Pitch was widely used in the ancient world to seal boats and containers. That practical detail gives the Ark description a recognizable ancient construction feature, even though the story is theological rather than a surviving technical manual.
The verse does not identify a modern commercial product or provide a precise recipe. Some translations use “bitumen,” “tar,” or related terms, but “pitch” is the traditional English answer matching the familiar wording. The key point is that the coating was applied to both surfaces, not only to the outside.