In Genesis, pitch was used to seal Noah's Ark and keep it watertight.
Genesis 6:14 instructs Noah to coat the Ark with pitch inside and outside. Pitch is a thick, waterproofing substance historically made from tar-like natural materials or processed organic matter. Applying it to both surfaces would help protect the wooden structure from water entering through seams and joints.
The instruction is a practical construction detail within the story, alongside the Ark's wood, rooms, dimensions, decks, window, and side door. The biblical Hebrew word is related to terms for covering or atonement, and translations commonly render it as pitch or bitumen-like material.
Modern discussions sometimes focus on the Ark's size or animal capacity, but the sealing instruction is one of the narrative's clearest engineering details. The text does not specify the exact chemical source of the pitch.