Lightweight clothing does not stop the penetration of the sun's harmful rays. Granger's Sun Shield enhances clothing's ability to protect skin from harmful UVA and UVB rays with a convenient wash-in treatment. For perspective the Skin Cancer Foundation rates the sun protection of a cotton t-shirt at UltraViolet Protection Factor (UPF) 7. Depending on the fabric's weave Granger's Sun Shield can boost the UPF rating of warm weather clothing to a rating of 50. Leading sun protection studies recommend that a UPF level 30 should be the minimum when exposed to prolonged intense sunlight. Also Granger's Sun Shield extends the life of garments and even helps resist fabric fading brought on by intense exposure to sunlight.