According to Genesis, pitch was used to waterproof Noah’s Ark inside and outside.
Genesis 6:14 instructs Noah to cover the Ark with pitch “inside and out.” The substance forms part of the construction instructions given before the Flood. Its purpose in the narrative is practical: sealing the vessel against water so that it could preserve Noah, his family, and the animals.
The Hebrew wording is commonly translated with a term related to pitch or bitumen, a waterproofing material known in the ancient Near East. English Bible versions may differ slightly in how they translate the word, but “pitch” is the standard concise answer.
This detail is separate from the wood specification. Genesis identifies the Ark’s wood as gopher wood and separately says that it must be coated with pitch. A common mistake is to name wood, tar, or resin as though those were the same instruction; the material used for sealing was pitch.