What is the primary source of thermal insulation used by fur seals to survive in cold ocean waters?

Answer

Their coat/fur

For fur seals, fur is the principal defense mechanism for insulation against the cold, consisting of an outer layer of coarse guard hairs and a crucial inner layer of soft fur.

What is the primary source of thermal insulation used by fur seals to survive in cold ocean waters?
mammaladaptationPinnipedFur Seal