Ultraviolet Protection Factor (UPF) Measurement

The depletion of the ozone layer in the Earth's atmosphere has been in the news frequently, and most people are aware of this serious problem. The extraterrestrial solar spectrum includes UVC (100 to 280 nm), UVB (290 to 315 nm), and UVA (315 to 380 nm) radiation. However, due to absorption by the ozone layer in the upper atmosphere, no UVC and only a fraction of UVB reach the Earth's surface. Therefore, any depletion of the ozone layer could lead to an increase in solar UVB levels at the Earth's surface.

Much of this ozone depletion has been attributed to the release of man-made fluorocarbons, which react with ozone, particularly high in the stratosphere, reducing the amount of ozone available to protect against incoming solar ultraviolet radiation (UVR). A 1 percent decrease in the ozone layer could lead to an increase in solar ultraviolet radiation at the Earth's surface and ultimately an increase in skin cancer.

Sunlight contains many different types of rays. The rays most damaging to human skin are called ultraviolet (UV) rays. There are two main types of ultraviolet rays that reach the Earth's surface: UVB and UVA. UVB rays cause sunburn and also play a major role in the development of skin cancer. UVA rays also play a role in the development of skin cancer. Additionally, UVA rays penetrate deeper into the skin and play a greater role in premature skin aging.

Sunlight contains approximately 500 times more UVA rays than UVB rays. Therefore, protecting your skin from the harmful effects of both UVB and UVA rays is crucial. Traditional chemical sunscreens have been more effective at blocking UVB rays than UVA rays.

Ultraviolet protection factor (UPF) is a standard measure used to measure the effectiveness of textiles in protecting skin from harmful ultraviolet (UV) radiation. As awareness of the health risks associated with UV exposure, such as skin cancer, premature aging, and sunburn, grows, so too has the demand for UV-protective clothing.

The ultraviolet protection factor (UPF) indicates how much UV radiation a fabric allows to pass through to the skin. For example, a fabric with a UPF of 50 allows only 1/50th (2 percent) of UV radiation to penetrate. This means it blocks 98 percent of UVA (315-400 nm) and UVB (280-315 nm) rays. Higher UPF values ​​indicate greater protection. Unlike the sun protection factor (SPF), which applies to sunscreens, the ultraviolet protection factor (UPF) is used specifically for textiles and accounts for both UVA and UVB radiation.

UV radiation from the sun is a leading cause of skin damage, including the deadliest form of skin cancer. Textiles with a high UV protection factor (UPF) value act as an effective barrier, reducing the need for frequent sunscreen reapplication and providing consistent protection during prolonged outdoor exposure. UV protection factor (UPF) testing benefits consumers, manufacturers, and regulators by ensuring that fabrics meet safety standards and perform reliably in real-world conditions.

Ultraviolet protection factor (UPF) is measured using in vitro techniques, primarily involving laboratory-based spectrophotometric analyses. These methods calculate a fabric's protective properties by evaluating the transmittance of UV radiation passing through a fabric sample.

The most commonly used method for measuring UV protection factor is spectrophotometry. It involves analyzing the amount of UV radiation transmitted through a fabric, both UVB (280-315 nm) and UVA (315-400 nm), in the wavelength range of 280-400 nm. A spectrophotometer measures the fabric's spectral transmittance, and this value is used to calculate the UV protection factor. The result is adjusted by extracting a 95 percent confidence interval and rounding to the nearest multiple of five to provide conservative ratings.

To ensure accuracy, fabrics are tested under standard conditions:

• Sample preparation: Representative samples are cut from different batches to account for variability. Samples are conditioned to stabilize humidity and temperature.
• UV exposure: Fabrics are exposed to controlled UV radiation using xenon arc lamps or other UV sources that simulate sunlight.
• Real-world simulations: Some tests evaluate the ultraviolet protection factor under conditions such as stretching, wetting, or accelerated aging (e.g., after washing or prolonged sun exposure) to mimic real-life use.

While in vitro spectrophotometry is the standard, there are other methods used to determine the ultraviolet protection factor:

• In vivo testing: Measures the minimal erythema dose to fabric-shielded and unshielded human skin using simulated solar radiation. This method is less common due to ethical and practical constraints.
• Dosimetry: Uses chemical or biological dosimeters (e.g., polysulfone films) to measure UV transmission under real-world conditions. This method accounts for scattered radiation, which can result in higher UPF values ​​compared to laboratory tests.

Many textile properties affect the UV protection factor, making its measurement a complex process. Factors affecting the UV protection factor include:

• Fiber type: Synthetic fibers like polyester generally provide better UV protection than natural fibers like cotton, thanks to their natural UV-blocking additives.
• Fabric structure: Tighter weaves (e.g., twill) and higher fabric density reduce UV transmission compared to loosely woven or knitted fabrics.
• Dyeing and finishing: Darker dyes and UV-blocking finishing (e.g. nanoparticle coatings) increase the ultraviolet protection factor by increasing the absorption or reflection of UV rays.
• Conditions of use: Wet or stretched fabrics generally have lower UV protection factors due to increased porosity. Ageing from washing or sun exposure can also degrade UV protection. Worn, stretched, or wet fabrics may lose UV protection.

To ensure consistency, several international standards have been developed for measuring UV protection factor. For example,

• One such standard is the "AS/NZS 4399 Sun protective clothing - Evaluation and classification." This standard measures the ultraviolet protection factor in the UVA and UVB range (290-400 nm). It requires testing in both dry and wet conditions.
• The standard is "AATCC TM183 Test Method for Transmission or Blockage of Erythema-Weighted Ultraviolet Radiation by Fabrics." This standard measures textile UV transmittance using a spectrophotometer (280-400 nm). It includes the calculation of UPF, UVA, and UVB blocking percentages.
• The standard “EN 13758-1 Textiles - Sun UV protective properties - Part 1: Test method for clothing fabrics” provides test methods for determining the ultraviolet protection factor of fabrics.
• The standard "GB/T 18830 Textiles - Evaluation of protective properties against solar ultraviolet radiation" is similar to the standard EN 13758, but with Chinese solar spectral weighting. An "ultraviolet protection factor of at least 40" is defined as qualified protection.

Consequently, measuring the ultraviolet protection factor (UPF) is a critical tool for assessing the UV protection capabilities of textiles, ensuring consumer safety and product reliability. Through precise methods like spectrophotometry and adherence to global standards, manufacturers are developing high-quality UV-protective clothing that meets the growing demand for sun safety. As innovations like UV-blocking additives and smart fabrics emerge, UVF testing continues to evolve, providing enhanced protection against the sun's harmful rays.

Our organization, which has been serving businesses for many years and meticulously following global developments in science and technology, employs a team of experienced professionals and a broad infrastructure to conduct testing, measurement, and analysis in a wide range of areas for businesses across all sectors. We also provide ultraviolet protection factor (UPF) measurement services.