According to Genesis, Noah covered the Ark with pitch to make it watertight.
Genesis 6:14 instructs Noah to cover the ark “inside and out” with pitch. In the Hebrew text, the related wording connects the coating with waterproofing, allowing the vessel to withstand the Flood waters described later in the narrative. The instruction applies to both surfaces rather than merely decorating or sealing the outside.
Pitch is a general term for a sticky, waterproofing substance derived from bitumen or similar materials. The verse does not identify a precise chemical recipe or tell readers exactly how it was processed. Consequently, modern reconstructions should not assume that the biblical pitch was identical to one particular modern product.
The coating is a separate detail from the ark’s building material, which Genesis identifies as gopher wood. It is also separate from the vessel’s dimensions and three decks. Together, these details form the short construction specification given in Genesis 6.