An immobilization system for a body, or body part, is provided, having a fixed form support and one or more shells that generally form an outlining structure of the body part to be immobilized. A formable support, having minimal mass, is molded and interposed between the fixed form support and shells to form a closely fitted support for the body part. The shell or shells may be removed from the system after molding, so that patient comfort is improved and total mass of the system is reduced, without compromise of the degree of immobilization. A retention mask, which also may be molded to conform to the body or body part, may be utilized to further stabilize positioning of the system.
