The sea is not humankind’s natural environment, and from ancient times people have taken steps to ensure their own survival on the water. There are records of primitive life jackets made from the inflated bladders of animals, and hollow gourds were sometimes used by people crossing rivers. Later, it was noticed that cork was extremely buoyant, and the first recognisable lifejackets emerged in the 1700s and were advertised in magazines for gentlemen.
The man in the illustration above has a cork life jacket and is holding a hollow ball which would also float.
In China, it was noted more than 1000 years ago that bamboo was extremely buoyant due to the internal structure, which has numerous separate watertight divisions. This inspired the design of Chinese junks, which have a number of transverse bulkheads dividing the hull into watertight compartments – an idea which the European designers of RMS Titanic had still not adopted in the twentieth century.