The durability of polymeric encapsulation materials was examined using outdoor exposure at the nominal optical concentration of 500 suns. The results for 12 months' cumulative field deployment are presented for materials including ethylene-co-vinyl acetate, polyvinyl butyral (PVB), ionomer, polyethylene/polyoctene copolymer, thermoplastic polyurethane, poly(dimethylsiloxane), and poly(phenyl-methyl siloxane). Measurements during the experiment included optical transmittance (direct and hemispherical), mass, visual appearance, and fluorescence spectroscopy in addition to the initial thermogravimetry of the materials. Measurements of the field conditions and ultraviolet dose at the test site were facilitated by numerous laboratory instruments; characterization of the specimen temperature was performed using thermography. Discovery experiments identified the importance of a secondary homogenizer optic and the importance of contamination control. To date, the formal experiment verified a thermal-runaway-motivated combustion failure mechanism for one of the PVB formulations and identified densification, cracking, and haze-formation behaviors in some of the silicone specimens. The behaviors observed for the silicone specimens may be facilitated by their greater thickness. Copyright © 2012 John Wiley & Sons, Ltd.