What type of filament did Thomas Edison use in a successful 1879 incandescent lamp?

Thomas Edison used a carbonized cotton thread filament in a successful 1879 incandescent lamp.

Edison and his Menlo Park team tested many filament materials while seeking a lamp that could glow for a useful length of time in a high vacuum. In October 1879, a carbonized cotton thread remained alight for roughly 13.5 hours, an important improvement over earlier experiments.

The filament was not the only key to the lamp. Edison’s system also required a suitable glass bulb, a reliable vacuum, electrical connections, and a distribution network that could supply many lamps. Later experiments used other carbonized materials, including bamboo, which could last substantially longer.

A common misconception is that Edison invented the first incandescent lamp from nothing. Earlier inventors had produced incandescent lamps, but Edison helped develop a practical, durable, commercially supported lighting system.