According to Genesis, Noah used pitch to waterproof the Ark.
Genesis 6:14 tells Noah to cover the ark inside and outside with pitch. The instruction follows the command to build the vessel from gopher wood, creating a distinction between its structural material and its waterproofing coating.
In biblical translations, the Hebrew term is associated with bitumen or pitch, a sticky waterproofing substance used in the ancient Near East. Bitumen was naturally available in parts of the region and could be used to seal boats, baskets, and buildings against water.
The story does not specify the exact application method, thickness, or quantity. It also does not say that the ark was made from pitch; the wood formed the vessel, while pitch sealed its surfaces. Modern depictions sometimes emphasize pitch as black tar, but the ancient material could vary in color and consistency.