boning in corsets. Whalebone is actually whale baleen, the cartiledge from a whale’s mouth. It was basically stiff, but had enough flexibility or elasticity to work well with curves. Unlike modern plastics which have been used to replace it today, whalebone would not re-shape with body heat or vary with air temperature.
(Whalebone is actually whale baleen, cartilege from a whale’s mouth as shown in this diagram and in real life)