The transmission spectra of thin films of the following materials have been measured between 2.2&mgr; and 14.8&mgr;: crude rubber, soft and hard vulcanized rubber, thermoprene, polyvinylchloride, Neoprene and Pliofilm. The spectrum of rubber resembles that of the long chain paraffins more closely than do those of the polymers, polyvinylchloride, Neoprene and Pliofilm, all of which contain chlorine and have distinctive spectra. Vulcanization of rubber with 2.3 percent sulfur gives rise to no new bands in the region 2.2&mgr; to 12.5&mgr; characteristic of molecular cross bonding. Some of the bands in these materials are identified with valence vibrations.