In the biblical account, Noah’s Ark was coated with pitch to make it watertight.
Genesis 6:14 instructs Noah to make the ark from gopher wood and to cover it with pitch inside and out. Pitch is a waterproofing substance, commonly associated with bitumen or a tar-like material in ancient construction. The coating would help seal the vessel against water.
The Hebrew term translated as “pitch” is related to the idea of covering or atonement, and translations vary in how they render some of the surrounding building terms. “Gopher wood” is also unidentified, so the text gives a specification without allowing a certain modern identification of the timber.
Pitch should not be confused with the ark’s structural material. Wood formed the vessel, while pitch served as the protective sealant. Nor does the passage describe modern fiberglass, paint, or metal reinforcement; those belong to later reconstructions and artistic models.