The optical properties of a cyclic olefin copolymer, Topas™, made by Celanese AG, are presented. This class of materials is attractive on account of their high use temperature, excellent optical transmission, low birefringence, and low moisture uptake. These materials are compared with other commonly used thermoplastics, namely, polycarbonate and polymethyl methacrylate. Finally, Topas™ is compared with a number of other optical polymers being studied for optical waveguiding applications. It is found that at 830 nm Topas™ has low losses (less than 0.5 dB/cm), so that it may be useful for datacom applications. At the telecommunication wavelength of 1550 nm the losses are in the range of 0.7 dB/cm. © 2001 Society of Photo-Optical Instrumentation Engineers.