According to Genesis, pitch was placed on the Ark’s inside and outside to make it watertight.
Genesis 6:14 tells Noah to cover the Ark with pitch inside and outside. Pitch is a thick, waterproofing substance historically made from natural bitumen, tar, or resinous materials. The biblical instruction therefore combines a wooden structure with a sealing coating.
The Hebrew wording creates a notable translation detail: the verb related to covering or sealing is connected with the noun often translated “pitch.” Some translations describe the instruction as coating the vessel with bitumen or waterproofing it with resin. Despite the wording differences, the practical purpose is clear: prevent water from entering.
Pitch is not the same thing as gopher wood, the material named for construction. It is also not described as a fuel, paint, or adhesive for building the Ark’s frame. Modern reconstructions often use contemporary marine sealants, but those are substitutes rather than materials named in Genesis.