In Genesis, Noah used pitch to seal the Ark against water.
Genesis 6:14 instructs Noah to cover the Ark inside and outside with pitch. The instruction appears alongside the command to build the vessel from gopher wood, but pitch serves a different purpose: it is the waterproofing material applied to the Ark’s surfaces.
The Hebrew word translated as “pitch” is related to a term for covering or atonement in some discussions of the passage, though translations generally render the construction instruction as pitch. The biblical text does not identify a modern chemical formula or specify the precise botanical or geological source of the substance.
This answer is distinct from the material used to construct the Ark. Gopher wood is named as the building material, while pitch is the coating used to make the vessel watertight. It is also distinct from tar-like products mentioned in later descriptions of ancient boats. The Genesis account gives the functional instruction without providing a modern engineering specification.