When a bone is fractured, it is usually put in a cast for several weeks to help hold it in place so that it can heal naturally. Most casts need to be kept clean and dry in order to promote healing and lower the risk of infection or other complications. This can be difficult, however, especially where bathing and swimming are concerned. Waterproof casting lets a person shower and swim regularly, even soon after breaking a bone. Waterproof casts, which are made of fiberglass, keep the limb immobilized for optimal healing but cause minimal disruption to a patient's daily routine. Waterproof casts are also lighter and less bulky than traditional plaster of Paris casts.
Most waterproof/fiberglass casts start out as soft, dry rolls of material that are impregnated with polyurethane resin. When water is applied to the material, it activates the resin, which hardens the material within 3 to 4 minutes. Placed beneath the fiberglass is layer of soft protective material, which, in addition to making the cast comfortable, dries it out properly so that it retains its shape and facilitates healing.
Allowing the cast to dry completely after exposure to water is important to keep the skin beneath it healthy. However, waterproof casts can eventually thin, making them inappropriate for treating certain types of fractures.
And, although ideal for swimming in a pool or showering, waterproof casts should not be used at the beach, because sand and other irritants can easily become lodged under the cast, leading to irritation and discomfort.