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This study investigated the use of two instruments to measure the ultraviolet protective factor (UPF) of T-shirt knit fabrics. After various laundering treatments, specimens were cut and UPF was measured from the wale, course, and bias directions with the ISO MET® UV-Meter and the Cary UV-Visible Spectrophotometer. Similar results were found between the two instruments and among repeated measures. Before UPF measurement, the shirt fabrics were repeatedly laundered using various household detergents and laundering additives commonly available to consumers. Statistically significant effects on the mean UPF values were found related to type of fabric, type of detergent/laundry additives, number of repeated launderings, and interaction effects of combinations of the three factors. Consumers can improve the UPF of their cotton and cotton-blend clothing by using detergents with brightener and/or products containing ultraviolet absorbers. Conclusions and implications for educators and apparel and textiles industry are provided.