Ge 6:14 "Make yourself an ark of gopherwood; make rooms in the ark, and cover it inside and outside with pitch.
The ark was covered inside and out with pitch. It served as the coating for the Ark. No water could get inside the Ark, yes not even a single drop of the waters of judgment could get in.
It is a picture of the blood of Christ shed on the cross. In Christ, a sinner who seeks refuge will be completely secure from God's wrath and judgment, yes not one bit of condemnation will fall on him.