Carbon Fiber is a weapon camouflage skin featured s in Call of Duty: Black Ops II and Call of Duty: Advanced Warfare. As the name implies, equipping it makes the weapon look like it's made out of carbon fiber.
Call of Duty: Black Ops II
The Carbon Fiber Camouflage can only be unlocked after the Kryptek: Typhon Camouflage has been unlocked like all other camouflages.
Call of Duty: Advanced Warfare
Carbon Fiber reappears in Call of Duty: Advanced Warfare. For most weapons, it is unlocked by obtaining a certain amount of kills without using any perks. Launchers are the exception, which require destroying 5 Goliaths.