The function of a cast is to rigidly protect an injured bone or joint. It serves to hold the broken bone in proper alignment to prevent it from moving while it heals.
Casts may also be used to help rest a bone or joint to relieve pain that is caused by moving it (such as when a severe sprain occurs, but no broken bones).
Different types of casts and splints are available, depending on the reason for the immobilization and/or the type of fracture.
Casts are usually made of either plaster or fiberglass material.