Plastic warships and hide-covered coracles

What is the strangest material successfully used to build a vessel?

Plastic is the first suggestion. Animal-hide coracles are another example, though their effectiveness is left uncertain.

Plastic is suggested as a contender for the strangest successful boatbuilding material because warships have been made from it. Animal hides are another example, with people attempting to make coracles from them. How well those coracles worked remains uncertain. Almost any apparently waterproof material has attracted an attempt at boatbuilding.