In the biblical Noah's Ark story, pitch sealed the Ark against water.
Genesis instructs Noah to cover the Ark inside and outside with pitch. The substance is presented as a waterproofing material applied to the wooden vessel, helping explain how the Ark could remain afloat during the Flood narrative.
Pitch is a thick, tar-like substance associated with waterproofing and sealing. The biblical wording uses the same basic idea on both surfaces of the Ark, rather than describing paint, plaster, or a modern synthetic coating. Some translations use related terms such as bitumen, but “pitch” is the traditional concise answer.
The waterproofing instruction is separate from the Ark's construction material. Genesis calls the wood “gopher wood,” while pitch is the sealant placed over it. Confusing those two details produces an answer that sounds plausible but does not match the text. The passage also mentions compartments and a side door, showing that the Ark's design includes both structural and sealing instructions.