How to Test UPF Clothing: What You Need to Know

How do you test the UPF of clothing?

The only reliable way to test UPF clothing is through standardized laboratory testing that measures how much UV radiation passes through the fabric. While you can do simple at-home experiments to compare fabrics, they can't tell you whether a garment is actually UPF 30, UPF 50, or UPF 50+. For a verified UPF rating, you need controlled testing using specialized equipment.

How is clothing tested?

UPF, or Ultraviolet Protection Factor, measures how effectively fabric blocks ultraviolet radiation from reaching the skin. Testing works by measuring the amount of UV radiation that passes through a fabric sample and using those measurements to calculate its UPF.

In a laboratory, a fabric sample is placed between a controlled UV light source and a detector. The equipment measures UV transmission through the fabric across relevant wavelengths and compares it with the amount of radiation reaching the fabric without the textile.

One recognized method for this type of testing is AATCC TM183, which measures the transmission or blocking of erythemally weighted ultraviolet radiation through textiles.

The result is a numerical UPF rating. UPF 50+ is the highest classification used for labeling sun-protective textiles.

Can You Test UPF Clothing at Home?

Not accurately.

You may have seen UV beads, UV cards, or other DIY methods that demonstrate whether a fabric reduces UV exposure. These can be useful visual experiments, but they aren't standardized UPF tests and can't establish an official UPF rating.

That's an important distinction. A fabric can appear to block UV light without having enough information to claim a specific UPF rating.

If a brand says a garment is UPF 50+, look for information about how that claim was established and whether the fabric was tested by an independent laboratory.

What Affects UPF?

A fabric's UPF isn't determined by fiber type alone. Construction matters.

Factors including fabric density, thickness, yarn structure, color, stretch, moisture, finishes, and wear can all affect how much UV radiation passes through a textile.

This is why simply knowing that a garment is made from polyester, cotton, linen, or another fiber doesn't tell you its UPF rating. Two fabrics made from the same fiber can have very different levels of UV protection.

The condition of the fabric matters, too. Stretching, repeated laundering, and wear can change a textile's UV transmission over time.

What Should You Look For in UPF Clothing?

If you're shopping for sun-protective clothing, don't stop at the words “UPF” on the product page.

Look for a specific rating, such as UPF 50+, along with information about the testing method. Third-party laboratory testing provides additional confidence that the stated rating is based on measured performance rather than an unsupported marketing claim.

It's also worth looking at the garment itself. UPF 50+ only protects the skin covered by the fabric, so the cut, coverage, neckline, sleeves, and fit all matter.

A well-designed sun-protective garment considers both the fabric and how much skin it covers.

Why Testing Matters

At Some Sun, we believe UPF clothing should be treated like any other performance product: the claims should be supported by testing.

Our UPF fabrics are third-party tested using AATCC TM183 to verify their UV-protection performance. But testing is only one part of creating a garment.

We also consider the fabric's feel, breathability, construction, coverage, and how the garment fits into an everyday wardrobe.

Because the goal isn't simply to create clothing with a UPF number. It's to make sun protection something you actually want to wear. And ours is very easy to wear.

Take a look at our bestselling, cotton-feel UPF 50 shirts.

The Bottom Line

If you want to know how to test UPF clothing, the short answer is: use standardized laboratory testing. At-home UV experiments can demonstrate differences between fabrics, but they can't establish a reliable UPF rating.

When buying UPF clothing, look for a specific UPF rating, a recognized testing method, and transparency about the testing behind the claim.

Sources

• AATCC, TM183: Transmittance or Blocking of Erythemally Weighted Ultraviolet Radiation through Fabrics
• ASTM International, D6544: Standard Practice for Preparation of Textiles Prior to Ultraviolet (UV) Transmission Testing
• ASTM International, D6603: Standard Specification for Labeling of UV-Protective Textiles