Casting is a medical treatment that holds a broken or injured bone in place using a rigid shell while it heals. A cast wraps around the injured limb in layers, creating a protective structure that prevents movement at the fracture site. Most people wear a cast for six to eight weeks, though the exact timeline depends on which bone is broken and how quickly it mends.
How a Cast Helps Bones Heal
Broken bones need stillness to repair themselves. When a fracture is held stable, the body sends specialized bone-building cells to the break site, where they lay down new bone tissue directly across the gap. This is the fastest, most efficient form of healing. If the broken ends move around instead, the body takes a slower route, first building cartilage at the fracture site and then gradually converting it to bone over a longer period.
A cast provides that stability from the outside. It locks the joints above and below the fracture so the broken bone fragments stay aligned while new bone fills in the gap. The rigid outer shell absorbs forces from daily activity that would otherwise shift the healing bone out of position.
What a Cast Is Made Of
Two materials dominate: plaster and fiberglass. Both start as rolls of fabric that are dipped in water, wrapped around the limb, and left to harden.
Plaster casts use gypsum-coated bandages. They’re heavier, slower to dry, and weaker under stress. Testing shows that plaster loses significant holding strength with repeated bending, dropping by roughly 59% after just two cycles of the same load. Plaster also absorbs water readily, which makes it vulnerable to damage if it gets wet.
Fiberglass casts are lighter and roughly five to six times stronger in tension than plaster. They hold up better over time and resist impact far more effectively. The tradeoff is that fiberglass has a rough, mesh-like texture and requires gloves during application because the material sticks to bare hands. Fiberglass is the more common choice today for most fractures.
How a Cast Is Applied
A cast goes on in three distinct layers, each serving a different purpose. First, a soft fabric sleeve called a stockinette is rolled over the limb, extending well beyond both ends of where the cast will sit. This creates a smooth base layer against the skin. Next, soft padding (typically cotton rolls) is wrapped around the stockinette, overlapping each pass by about 50%. The padding cushions bony areas like the wrist, elbow, or ankle where pressure sores could develop. Finally, the outer casting material is dipped in room-temperature water until it stops bubbling, then wrapped over the padding in overlapping layers.
The casting material should never touch unpadded skin directly. Once all the layers are in place, the stockinette is folded back over the ends of the cast to create smooth, finished edges. The whole structure then hardens as it dries, forming a custom-fitted shell around the limb.
Living With a Cast
Traditional casts and moisture are a bad combination. A wet cast can trap dampness against the skin, leading to irritation, breakdown, or infection. Cover the cast with two layers of plastic sealed with a rubber band or tape before showering. Avoid swimming entirely in a standard cast. If it does get wet, a hair dryer on a low or cool setting can help dry the inner padding, but it may not fully solve the problem.
Itching is one of the most common complaints. Resist the urge to slide objects like pencils or knitting needles inside the cast to scratch. This can injure the skin or introduce bacteria. A hair dryer aimed into the cast on a cool setting can relieve itching without risking damage. Keep dirt, sand, powder, lotion, and deodorant away from the inside of the cast. Don’t pull out padding, trim edges, or make any adjustments yourself.
Waterproof Cast Liners
Newer waterproof liner materials offer an alternative to traditional cotton padding. These liners use synthetic fibers woven into a three-dimensional open structure that drains water quickly and allows body heat to evaporate remaining moisture. In a clinical trial comparing the two, 75% of patients preferred the waterproof version. Waterproof liners scored significantly better for odor and sweat, and physicians rated skin condition as healthier under the waterproof liner compared to cotton.
Both liner types maintained fracture alignment equally well, so the waterproof option doesn’t sacrifice any structural performance. Waterproof-lined casts also had fewer unscheduled cast changes. If getting a cast wet is a major concern for your lifestyle, asking about waterproof options is worth the conversation.
Warning Signs to Watch For
A cast that fits well at first can become problematic if the limb swells. The most serious risk is compartment syndrome, a condition where pressure inside the tissues builds to dangerous levels because the rigid cast won’t expand. Symptoms include pain that feels disproportionate to the injury, especially pain that persists even after taking pain medication. Tightness, visible swelling, numbness, tingling, or a burning sensation under the skin are all signals that pressure may be building.
If the injured limb feels fuller or firmer than usual, or if stretching the fingers or toes causes severe pain, the cast may need to be loosened or split. Compartment syndrome is a medical emergency when it occurs in its acute form, so these symptoms shouldn’t be waited out.
How a Cast Is Removed
Cast removal uses a specialized oscillating saw. The blade vibrates back and forth over a tiny angle rather than spinning in a circle. It needs resistance from a hard material to cut, so it slices through the rigid cast shell easily. When the blade contacts soft tissue like skin, there isn’t enough resistance for it to cut. The sensation can feel buzzy or warm, but the saw is designed not to injure the skin underneath. After the shell is cut along both sides, the padding and stockinette are snipped away with scissors.
3D-Printed Casts
3D-printed casts are an emerging option, particularly for wrist and hand injuries. These are custom-designed from a scan of the patient’s limb and printed as a rigid, ventilated shell with holes throughout the structure. Clinical reviews show that patients rate 3D-printed wrist splints higher than fiberglass for comfort, satisfaction, and perceived function, even though objective measurements of wrist function are similar between the two. For certain wrist fractures, 3D-printed splints have produced better alignment outcomes on imaging compared to traditional splints. Patients with chronic hand conditions also reported less pain and better hand function when switching from conventional splints to 3D-printed versions.
The open lattice design solves many of the daily frustrations of traditional casts. The skin can breathe, the cast can get wet without consequence, and itching is far less of an issue. Availability is still limited compared to standard casting, but the technology is increasingly used in orthopedic clinics.