In the biblical Noah's Ark story, pitch was used to waterproof the Ark.
Genesis instructs Noah to cover the Ark with pitch inside and out. Pitch is a sticky, tar-like waterproofing substance, and the instruction fits the practical need to seal a large wooden vessel against water. The Hebrew wording is related to terms for covering or coating, and translations commonly render it as pitch.
This material is different from the wood named in the same passage. Genesis describes the Ark as being made from gopher wood and then separately says it should be covered with pitch. Readers sometimes merge those two details or substitute modern marine sealants, but the biblical text names pitch. The passage does not identify a modern chemical formula or a specific tree species for the wood, so later attempts to reconstruct the vessel involve interpretation.