AbstractThe effectiveness of ultraviolet stabilizers of various types of polyolefin, cellulose ester, and poly (vinyl chloride) plastics was investigated. Most of these stabilizers were of the ultraviolet‐absorbing type but two were of the nonabsorbing type. Exposures were made both outdoors and indoors in a Twin‐Arc Weatherometer. The latter was modified by the addition of ten 20‐watt fluorescent sun lamps to remedy the short‐ultraviolet deficiency of the enclosed carb