If you ever break a bone, you'll probably need a cast to hold the pieces of bone steady while they're healing. Casts wrap around the broken area and can be made out of plaster, fiberglass, or even plastic and air (called an air cast). When you get a cast, you need to keep it away from water the entire time it's on. Even though a cast may look and feel a little clumsy, it lets your broken bone grow back together again, and that's pretty important! After you're better, the doctor will take the cast off, which doesn't hurt at all.