According to Genesis, Noah covered the Ark with pitch.
Genesis 6:14 instructs Noah to apply pitch inside and outside the vessel. Pitch is a waterproofing substance, traditionally associated with tar-like or bituminous materials, although the exact ancient product is not certain.
The instruction is practical as well as narrative: a large wooden vessel would need a sealed surface to keep water out. The text pairs the waterproofing command with the instruction to build the Ark from gopher wood.
Pitch is not the Ark’s timber, glue, or cargo. It is the coating used to protect the wooden structure. Translation choices can vary, with some versions using terms such as “bitumen” or “tar,” but “pitch” is the conventional concise answer in English.