Rose Frank L: Vacuum formed support structures and immobilizer devices. Bio Medical Systems, July 17, 1973: US3745998 (153 worldwide citation)

Rigidifiable and collapsible support structures are utilized as orthopedic casts and slings, litters, and stretchers, cervical collars and related devices, with two conditions or modes of operation, a collapsed condition in which they are easily molded and formed to conform to the contours of the hu ...