According to Genesis, Noah’s Ark was sealed with pitch inside and outside.
Genesis 6:14 tells Noah to cover the ark with pitch on the inside and on the outside. Pitch is a waterproofing substance made from a thick, tar-like material; in an ancient boat-building context, it would help reduce leakage through wooden joints and surfaces.
The instruction is separate from the ark’s wood. Genesis names gopher wood as the construction material and then gives pitch as the coating. English translations sometimes use terms such as bitumen or tar in related ancient contexts, but “pitch” is the familiar wording of the biblical instruction and the expected answer.
The passage does not identify the chemical composition of the pitch or describe the application process. Nor does it establish that a particular surviving archaeological coating belonged to Noah’s Ark. The detail is a construction specification within the Genesis narrative.