What is UPF?

UPF stands for Ultraviolet Protection Factor, which is a measurement of the sun protection strength of clothing and fabrics used in outdoor shades. It represents the ratio of UV radiation exposure with and without the protection of the measured textile.

What does UPF mean?

There are many factors that go into the calculation of UPF ratings, but at the end of the day you probably just want to understand what the numbers indicate. You might want to know, “what is UPF 50?” In this example, a fabric with UPF 50 will permit only 1/50th (2%) of ultraviolet radiation to pass through it.

What is a good UPF rating?

Obviously, the higher the UPF the stronger the protection. However, there are levels of protection that you should be aware of as you evaluate textile for patio umbrellas, shades and outdoor clothing [Bilimis 2011].

Levels of UPF Protection

UVR ProtectionUPF RatingUVR %
Moderate10 to 1910 to 5.1
High20 to 295.0 to 3.4
Very High30 to 493.3 to 2.0
Maximum50+< 2.0

What’s the difference between SPF and UPF?

SPF is short for Sun Protection Factor, which is used to measure the effectiveness of sunscreen and other products. It is a time-related measurement relative to your skin’s natural tendency to burn. A sunscreen with an SPF rating of 30 provides 30 times more protection against UVB rays than if you wore no sunscreen at all. So, if you have fair skin and tend to burn after 10 minutes, applying SPF 30 sunscreen will allow you to be exposed for up to 300 minutes without burning. As mentioned above, UPF measures the UVA and UVB radiation that penetrates a textile and reaches the skin.

What’s the difference between UVA and UVB radiation?

What's the difference between UVA and UVB radiation?

  • UVA rays account for nearly 95% of the ultraviolet radiation that reaches the earth’s surface. They penetrate deep into the skin’s dermis and over time can lead to premature aging of the skin, cause wrinkles and suppress the immune system. Recent studies have shown that UVA rays also damage skin cells in the lower layer of the epidermis, where most skin cancers develop. These rays can penetrate cloud cover and glass.
  • UVB rays are more intense, but far less prevalent that UVA rays. They are the primary cause of skin reddening, sunburn and other superficial damage to the skin’s outer epidermal layer (e.g. tanning, photo-aging, etc). UVB radiation plays a significant role in the onset of skin cancer. These rays do not penetrate glass to any measurable degree, but they do bounce off of reflective surfaces, so they can burn you when you are under cover or during icy winter months.

[Soter 2017]

What characteristics affect a fabric’s UPF?

  1. Weave – The tighter the fabric is woven together, the less UV radiation passes though
  2. Color – Dark colors of identical fabric types absorb ultraviolet rays more strongly than their lighter shades, which increases the sun protection
  3. Weight – A heavier version of the same fabric will be minimally more protective against UVR
  4. Stretch – The greater the stretch or tension put on a textile, the lower the UPF rating
  5. Water – Some fabrics, such as polyester and cotton, provide less protection against UVR when they have absorbed water
  6. Washing – Cotton-based fabrics tend to shrink after the first washing, thereby tightening the weave and reducing the transmitted ultraviolet radiation
  7. Additives – UVR stabilizers or additives can be used to improve the sun protection of a variety of textiles

[Gies, Roy, Toomey, & McLennan 1998]

References

Additional Resources

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