Genesis says Noah coated the Ark with pitch to make it waterproof. The instruction appears in Genesis 6:14, which tells him to cover the vessel inside and outside.
Pitch was a general ancient waterproofing substance rather than a uniquely identified modern product. In the ancient Near East, bitumen and related materials were used to seal boats, baskets, buildings, and other objects against water. The biblical text does not specify the chemical composition of Noah’s pitch.
This detail is separate from the Ark’s building material. Genesis names gopher wood for construction and pitch for sealing. Later translations may use terms such as bitumen, tar, or resin, reflecting uncertainty about the precise ancient substance. The central idea remains that the Ark was coated on both sides to protect its wooden structure from flooding.