What was the initial breakthrough carbonized material that gave Edison's team about 13.5 hours of light in late 1879?

Answer

Carbonized cotton thread.

The initial successful test involved using carbonized cotton thread, which provided a significant leap in performance by lasting over thirteen hours.

What was the initial breakthrough carbonized material that gave Edison's team about 13.5 hours of light in late 1879?
inventionbulbelectricityEdisonfilament