Telecommunications wires, fibers, and cables exposed to the elements expand and contract daily due to variations in ambient temperature from day to night. Aerial cables suspended from poles stretch during the warmth of the day, with the weight of the cable magnifying the effect, and shrink in the cool of the night. Copper cables are more susceptible than glass fiber optic cables, but both stretch and shrink to some extent. As they do so, the length of the path increases and decreases, and signal propagation delay increases and decreases slightly. As a result, high speed digital systems can suffer timing problems that can cause losses of synchronization and, ultimately, temporary system failures. See also propagation delay.