By immobilizing the patient from the neck to the hips, pressure is distributed evenly, taking excess pressure off overloaded or unstable areas. These jackets were originally made of plaster of Paris, but now are typically made out of molded plastic. These belts are designed to reduce low back strain and muscle fatigue that can occur when you are lifting heavy objects. The belt circles around the waist, covering the lumbar region of the spine, and closes in front. These belts are usually made of cloth or canvas and do not have stays.
Some models also have lordosis pads.
Braces, belts, and jackets are designed to immobilize and support the spine when there is a condition that needs to be treated. More specifically, lumbar corsets and braces compress the abdomen, which increases the intra-abdominal pressure. This act allows pressure on the vertebral column to unload, providing some relief. There are other reasons bracing is used. One is the theory that they insulate the skin, producing increased warmth that decreases the sensation of pain - much like a heating pad.