According to Genesis, Noah coated Noah’s Ark with pitch to make it watertight. Genesis 6:14 tells him to cover the vessel inside and outside with pitch. The instruction appears immediately after the command to build the Ark from gopher wood.
Pitch is a general term for a thick, waterproofing substance, often associated with bitumen, tar, or resin. Ancient boatbuilders used such materials to seal seams and protect timber from water. The Hebrew wording is related to the broader idea of covering or coating, so translations may differ slightly in how they describe the substance.
A common mix-up is answering “tar,” which is a reasonable modern gloss but not the conventional wording of many English Bible translations. “Pitch” is the concise answer that matches the familiar Genesis text. The passage does not identify a specific geological source or chemical formula for the waterproofing material.