According to Genesis, Noah’s Ark was coated with pitch inside and out.
Genesis 6:14 instructs Noah to make the ark from gopher wood and to cover it with pitch, both inside and outside. Pitch is a waterproofing substance made from bitumen or a similar tar-like material. Its purpose in the narrative is to seal the wooden structure against water during the flood.
The Hebrew term translated as pitch is related to words for covering or atonement in some linguistic discussions, although translations differ in how they render the material. English Bibles commonly use “pitch,” “bitumen,” or “tar.” These terms describe the same general waterproofing function rather than a precisely identified modern industrial product.
The verse also mentions rooms, a door in the side, and three decks. It does not provide a construction manual, identify the species meant by “gopher wood,” or explain how the coating was applied. Those details are often expanded in artwork and retellings but are not specified in Genesis.