Genesis says Noah sealed the Ark with pitch inside and outside.
Genesis 6:14 instructs Noah to cover the Ark with pitch on the inside and the outside. Pitch is a dark, sticky waterproofing substance historically obtained from natural sources such as wood tar or bitumen. In the story, it helps make the large vessel watertight.
English translations differ slightly in how they render the underlying Hebrew wording, but the central instruction is consistent: the Ark is to be coated to prevent water from entering. The pitch is not the same material as the wood named in the verse; gopher wood describes the construction timber, while pitch describes the sealant.
The biblical text does not specify a recipe, quantity, or exact ancient manufacturing process. Readers should therefore avoid treating the passage as a complete technical construction manual. It gives selected dimensions, compartments, timber, and waterproofing instructions within the narrative.