Noah used pitch to cover the Ark inside and out, according to Genesis.
Genesis 6:14 tells Noah to make the Ark from gopher wood and to cover it with pitch inside and outside. Pitch is a waterproofing substance, generally understood as a bitumen-like or resinous material, though the precise ancient substance cannot be identified with certainty from the English word alone.
The instruction explains how the wooden structure was to be sealed against water. It does not mean that the Ark was made from pitch; the text distinguishes the building material from the coating. Nor does Genesis give a detailed recipe, thickness, or application method.
Translations differ in how they render the underlying Hebrew term, but “pitch” is the standard English answer in many Bible translations. The material is a construction detail, distinct from the Ark’s dimensions, decks, door, and window. Those details appear together in Genesis 6 but answer different questions.