For the bow, the only real maintenance is regular cleaning of the stick with a cloth (to remove rosin dust), re-hairing, and replacing the leather and silver wire wrapping. In the course of playing, hairs are often lost from the bow, making it necessary to have it rehaired periodically, which is done by professionals at roughly the cost of a new set of strings. Other maintenance may include replacing the wire lapping and leather grip or lubricating the screw. Large cracks and breakages in the bow are usually fatal; they cannot be repaired like the body of the violin can. A bow which has warped and is no longer straight can sometimes be bent back to true or re-cambered, but this must be done with heat by a craftsman and is not always successful or worthwhile. Loosening the hair when the bow is not being used helps keep the bow from becoming "sprung" or losing its camber and the hair from becoming stretched. In the 2020s, there are bows available made from fiberglass or carbon composite which are less fragile. Some of the fiberglass bows are much cheaper than wooden bows. The best carbon composite bows are used by some professional musicians.