Traditional shoelaces were made of leather, cotton, jute, hemp, or other materials used in the manufacture of rope. Modern shoelaces often incorporate various synthetic fibers, which are generally more slippery and thus more prone to coming undone than those made from traditional fibers. On the other hand, smooth synthetic shoelaces generally have a less rough appearance, suffer less wear from friction, and are less susceptible to rotting from moisture. Specialized fibers like flame resistant nomex are applied in safety boots for firefighters.