According to Genesis, Noah coated the Ark with pitch inside and out.
Genesis 6:14 instructs Noah to make the vessel waterproof by applying pitch to both its interior and exterior surfaces. In biblical translations, the Hebrew term is commonly rendered as “pitch,” a waterproofing substance associated with bitumen or asphalt. The instruction appears immediately after the Ark’s construction materials are specified: gopher wood, or a similar traditional translation.
Pitch was a practical choice for sealing wooden vessels in the ancient Near East. Bitumen deposits were known in the region, including areas around Mesopotamia, where natural asphalt could be collected and used for construction and waterproofing. The biblical account does not give a chemical recipe or identify a particular tree resin.
This detail is sometimes confused with the Ark’s building material. Genesis names wood for construction and pitch for waterproofing; pitch is not the wood itself. The same general waterproofing idea also appears in other ancient flood traditions, although their wording and construction details differ.