Genesis says Noah sealed the Ark inside and outside with pitch.
In Genesis 6:14, God instructs Noah to build the Ark from gopher wood and to “cover it inside and out with pitch.” Pitch is a waterproofing substance, generally understood as a bituminous or resinous material used to make a vessel watertight. The instruction is practical within the narrative because the Ark is described as a huge enclosed craft intended to survive prolonged flooding.
The precise identity of “gopher wood” is uncertain, but the text is explicit about the coating material. Pitch should not be confused with tar in every modern translation, since English versions use different terms for the Hebrew word. Nor does the passage provide a modern construction recipe or identify a specific tree species. The key detail is that both the interior and exterior were coated, rather than only the outside surface.