Carbon has the highest resistivity of all the elements—it’s resistivity is over 100 times greater than that of a metal such as platinum. To create the carbon filaments, Edison partially burned different materials until the material changed into carbon. Because carbon filaments could be very fragile, Edison used a looped filament, rather than a coiled filament. The filaments were shaped in molds before they were carbonized.

Edison co-workers experimented with a variety of different types of bamboo, including Calcutta bamboo and Japanese Bamboo. Japanese bamboo turned out to work better than the Calcutta bamboo.