According to Genesis, Noah covered the ark with pitch inside and outside.
Genesis 6:14 instructs Noah to build the ark from gopher wood and to cover it with pitch. Pitch is a thick, sticky waterproofing material historically obtained from natural bitumen, tar, or resinous substances, depending on the technology and terminology of the period. The biblical instruction emphasizes sealing the vessel against water.
The Hebrew word translated as “pitch” is related to the language of covering or atonement in some discussions, but the immediate construction context is practical: the ark’s surfaces are to be coated. Genesis does not provide a recipe, thickness, or precise geological source for the material.
Pitch is sometimes confused with the ark’s wood because both appear in the same verse. They serve different purposes: gopher wood is the stated building material, while pitch is the waterproof coating. The passage also mentions internal compartments and multiple decks, but pitch is the specific substance used to seal the vessel.