Hair fibers can make thin hair look thick and also conceal the bald spots due to hair loss. Made with colored protein, Toppik's Dark Brown Hair Building Fibers blend in with the original hair. The hair building fibers in dark brown are ideal for individuals who have natural deep brown hair with red undertones. This is a natural shade that matches the original dark brown and red tones of the natural hair. These hair fibers are resistant to water, humidity and sweat, and as a result they last longer.