Vitreous infrared transmitting materials were drawn into coated and uncoated fibers by employing techniques developed for the formation of visible radiation transmitting glass coated-glass fiber. Infrared transmitting fiber was fabricated from germanate, silicate and arsenic trisulfide. Crystalline sodium chloride was extruded into relatively large diameter fiber. Plastic materials such as the epoxies and lucite are shown to be suitable potting materials for uncoated fiber. Absorption bands of these materials do not seriously influence the transmitted radiation, however, compounds having few absorption bands are to be favored. The performance of fibers of diameter comparable to the wavelength of the transmitted radiation is analyzed by using dielectric waveguide theory, and the results are interpreted from the optical viewpoint of thin film interference and frustrated total reflection.