Ultraviolet Protection Factor (UPF) indicates how much UV radiation (both UVB and UVA) a fabric allows to reach your skin. For example, a UPF 50 fabric blocks 98 percent of the sun’s rays and allows two percent (1/50th) to penetrate, thus reducing your exposure risk significantly.
UPF: What it is and why it matters
What you need to know: A fabric must have a UPF of 30 to qualify for The Skin Cancer Foundation’s Seal of Recommendation. A UPF of 30 to 49 offers very good protection, while UPF 50+ rates as excellent.
How does UPF differ from SPF?
UPF measures the amount of UV radiation that can penetrate fabric and reach your skin. Sun Protection Factor, or SPF, is based on the time it takes for UV-exposed skin to redden; if you burn after 20 minutes, if used correctly, an SPF 15 sunscreen may protect your skin 15 times longer.
Another important distinction: UPF measures both UVB and UVA rays, while SPF measures only UVB.