carbon fiber

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An extremely strong thin fiber made by pyrolyzing synthetic fibers, such as rayon, until charred. It is used to make high-strength composites.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A very strong filament made by the pyrolysis of a synthetic fiber such as rayon.
• noun A cloth or felt made from these fibers.