Measuring the UV protection factor (UPF) of fabrics and clothing

Importance of Topic

Ozone layer depletion has increased the amount of biologically active ultraviolet radiation (UVR) reaching the Earth’s surface, raising concerns about skin damage and cancer risk. Textiles and clothing serve as a primary barrier to UV exposure, but their protective performance varies widely depending on fabric structure, fiber content and treatments. Reliable measurement of Ultraviolet Protection Factor (UPF) helps manufacturers, regulators and consumers assess and compare the UV shielding capacity of garments.

Objectives and Study Overview

This application note describes a standardized spectrophotometric method to determine the UPF of six reference textiles with diverse constructions (woven vs. knitted) and fiber compositions (cotton, polyester, wool, nylon). Key goals include demonstrating a safe, reproducible laboratory approach and illustrating how spectral transmission data from 280 to 390 nm are translated into a quantitative UPF value.

Methodology and Instrumentation

The protocol employs an Agilent Cary 3E UV-Vis spectrophotometer fitted with a Cary 1/3E diffuse reflectance accessory (integrating sphere), a fabric holder and a Schott UG11 filter. Transmission spectra were recorded at 1 nm intervals across the UVB (290–315 nm) and UVA (315–380 nm) regions. Each textile was analyzed in both machine and cross-machine orientations, with eight sub-samples per fabric to ensure statistical robustness. An integrating sphere configuration coupled to the UG11 filter eliminates fluorescence artifacts and captures all forward-scattered and transmitted light. UPF values were computed using the equation that weights spectral irradiance by the erythemal action spectrum, and results were processed with the UPF Easy Menu software.

Main Results and Discussion

The six fabrics yielded a broad range of protection levels: one cotton weave fell below UPF 10 (not rateable), nylon and polyester knits provided moderate protection (UPF 10–19), a cotton knit and two woven polyester/wool samples achieved very high to maximum UPF (30+ and 50+). Spectral transmission profiles revealed that even small changes in weave density or fiber type can significantly alter UVB and UVA blockage. The statistical analysis (mean, standard deviation, 95% confidence limit) demonstrated method precision, with coefficients of variation below 10% for all samples.

Benefits and Practical Applications

• Non-invasive, laboratory-based UPF measurement avoids human subject testing and associated health risks.
• High spectral resolution allows identification of wavelength-dependent weaknesses in fabric UV shielding.
• The standard workflow and automated software reduce operator variability and accelerate throughput.
• Data support R&D in textile development, quality control and regulatory compliance.

Future Trends and Opportunities

Advances may include integration of UV sensors into wearable garments for real-time exposure monitoring, development of novel UV-absorbing treatments and coatings, and expansion of standards to cover visible light and infrared protection. Miniaturized spectroradiometric devices could enable on-site UPF verification for textile manufacturers and retailers.

Conclusion

The described spectrophotometric approach, combining the Cary 3E spectrophotometer, integrating sphere accessory and UPF Easy Menu software, offers a robust, user-friendly solution for assessing textile UV protection. It achieves high repeatability, captures the full erythemally relevant spectrum and eliminates safety concerns associated with in vivo testing.

References

1. Gies P. and Roy C. Ultraviolet radiation, ozone thinning, the environment and UPF testing. Proceedings SDCANZ Textiles and Sun Protection Conference, UNSW, 1993.
2. United Nations Environment Programme. Environmental Effects of Ozone Depletion. Nairobi, 1991.
3. Welsh C. and Diffey B. Protection against solar actinic radiation afforded by common clothing fabrics. Clin Exp Dermatol, 1981, 6:77–82.
4. CIE Research Note. Reference action spectrum for ultraviolet-induced erythema in human skin. CIE J., 1987, 6:17–22.
5. Menzies S. et al. Comparative study of fabric protection against ultraviolet-induced erythema determined by spectrophotometric and human skin measurements. J. Photodermatology Photoimmunology Photomedicine, 1992, 8(4):157–163.