We want to label our running tops "UPF 50+". What does that claim need behind it?
A UPF number on a label should come from instrumental testing and follow a labelling standard. ASTM D6603 sets the categories, required label elements and limits on medical claims.
Our new running tops use a tight polyester knit, and the mill says the fabric is "UPF 50+". We want to put that on the hang tag and product page. What do we need before we do?
Main answer
UPF, or ultraviolet protection factor, describes how much UV radiation a fabric lets through. It is measured instrumentally in a laboratory. In the US, ASTM D6603 is a specification for labelling UV-protective textiles. It describes what a UV-protective label must contain and the classification categories, and it sits on top of the normal care and fibre content labelling rules rather than replacing them. A mill's statement about its fabric is a starting point, but the claim on your product should rest on tests of your finished fabric.
What the label must show
Under ASTM D6603, a UV-protective label contains a UPF value, a protection category and a statement that the product is labelled according to the ASTM specification. The categories are Good, Very Good and Excellent UV protection, starting at a UPF of 15; fabrics below that are not labelled as UV-protective. The specification also says labels must not state or imply medical claims such as preventing skin cancer or skin ageing.
Why the number can be lower than expected
The labelled UPF is meant to reflect the lowest protection expected in use, so the standard bases it on specimens that have been prepared to simulate laundering and exposure, as well as unprepared ones. Stretch matters a great deal on knits: when the fabric is stretched across the shoulders or back, the gaps between yarns open and more UV gets through. Wet fabric can also behave differently. ASTM D6603 lists optional warnings about stretching, wetting and heavy wear that you may want to use.
What to ask the lab
Ask a lab to test your finished fabric, in the colours you will sell, to the method and specimen preparation referenced in ASTM D6603, and to state the label UPF and category. Dark and light colours of the same fabric can give different results. If the fabric or dye house changes, retest.
Product page wording
Use the same value and category online as on the label. Avoid adding broader claims, and note that only skin covered by the garment is protected. If you also make moisture-management claims, those need their own test methods, such as the AATCC moisture management methods.
Keep test reports by style and colour so you can answer a retailer or regulator who asks how the claim was supported.
Sources and further reading
- ASTM D6603 — Standard Specification for Labeling of UV-Protective Textiles
- ISO 6330:2021 — Domestic washing and drying procedures for textile testing
- AATCC — Moisture management methods (TM195, TM197, TM201, TM213)
Standards and rules are summarised from their published scope or official guidance. Use the current edition and confirm requirements for your market.
Three perspectives on this question
Purchasing perspective
I'd ask the mill for its UPF report on the exact article and colour, then budget for our own test on finished fabric before the claim goes to print.
Merchandising perspective
UPF is a strong selling point for running and outdoor ranges. I'd keep the wording to the value and category, and avoid health claims in campaign copy.
QC perspective
We'd check that bulk fabric matches the tested article and colour, and flag any dye lot or mill change that would need a retest.
Working on a similar program?Send your tech pack, fabric references and test requirements. We reply with a quote and the questions we need answered.
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