Abstract: The construction of a direct reading, ionization chamber dosimeter is almost exclusively of thermoplastic material. Except for an electrometer frame and switch contacts, the dosimeter comprises components of injection molded thermoplastic material. The dosimeter barrel and most of the structural components are made from either electrically conducting polycarbonate or non-conducting polycarbonate. Optical parts and lenses are formed from transparent plastic materials. The ionization chamber is made from polypropylene loaded with carbon black. The light-weight plastic construction of the dosimeter renders it relatively insensitive to mechanical shock and causes it to interact with ionizing radiation in a manner substantially similar to animal tissue or human flesh.