The Boeing Engineering and Construction Company (BEC) has been involved in the study and use of plastic films for solar collectors during the past four years. This paper summarizes experimental work accomplished by BEC, aimed at finding low cost, long life, highly specular plastic films for collector utilization. Primary investigations include contacting the plastic film industry for potential candidates, measuring the specularity, and initiating exposure testing of the most promising materials. Samples have been subjected to up to 18 months of solar exposure in both real and accelerated testing techniques at a desert test site in Arizona. The changes in mechanical and optical properties for each of the materials and test conditions are presented. Thermoformed plastic domes (35.5 and 61 cm diameter) have been exposure tested at the same desert site since late 1978. The testing was initiated to verify the weatherability of the various materials and processes of fabrication. Changes in mechanical and optical properties and dust accumulation are discussed.