Genesis tells Noah to waterproof the Ark with pitch.
Genesis 6:14 instructs Noah to cover the Ark with pitch inside and outside. Pitch is a thick, waterproofing substance associated with bitumen or tar in ancient construction. Applying it to both surfaces would seal the wooden structure and reduce the entry of water through joints and gaps.
The instruction appears alongside the order to build the Ark from gopher wood. These are separate details: gopher wood names the building material in the biblical text, while pitch supplies the protective coating. Genesis does not specify the exact chemical composition or how Noah manufactured the pitch.
Translations differ slightly in wording, using terms such as “tar” or “bitumen,” but “pitch” is the traditional English answer. The passage also tells Noah to make rooms in the vessel and gives its length, width, height, roof, and side door, making it one of the Bible’s most concentrated descriptions of the Ark’s construction.