In Genesis, Noah's Ark was coated with pitch inside and outside.
Genesis 6:14 instructs Noah to cover the Ark with pitch, using the same basic Hebrew root associated with covering or making waterproof. The coating was applied both within and without, according to the passage. This detail complements the command to build the vessel from gopher wood and to create compartments inside it.
Pitch is a general term for a viscous waterproofing substance, often associated with bitumen or resinous materials. The biblical text does not provide a laboratory recipe or identify the exact chemical composition. Ancient Near Eastern boatbuilders commonly used bitumen and related substances to seal wooden or reed vessels against water.
The term is sometimes confused with the Ark's construction material. Gopher wood refers to what the vessel was made from, while pitch refers to its protective coating. The story does not say that pitch was used as the structural framework. These are separate instructions in the same verse.