Parents shopping for children's swimwear have learned to look for three letters: UPF. A "UPF 50+" hangtag can decide a purchase — which is exactly why brands need to understand what the rating means and how it is verified before putting it on their products.
What UPF 50+ actually means
UPF stands for Ultraviolet Protection Factor. It measures how much UV radiation passes through a fabric. A UPF 50+ rating means the fabric blocks at least 98% of UV rays — only 1/50th gets through to the skin. The "+" indicates the fabric tested above 50 and the rating is capped there by convention.
Two things buyers often misunderstand:
- UPF is about the fabric, not the garment design. A UPF 50+ fabric in a short-sleeve top protects only the covered skin. Coverage — long sleeves, higher necklines — is a design decision that multiplies the value of the fabric.
- UPF is not the same as SPF. SPF rates sunscreens; UPF rates textiles. They are measured differently and should never be mixed on a label.
How factories test it
UPF is verified by laboratory testing of the fabric, not by looking at it. In practice, a serious factory follows this sequence:
- Fabric selection: tight-knit polyester or nylon/spandex blends with UPF-rated constructions. Darker colors and tighter knits generally test higher, but the rating must be measured, not assumed.
- Lab testing: fabric samples are sent to an accredited textile laboratory, which measures UV transmittance across the relevant spectrum and issues a UPF rating report.
- Report to buyer: the factory shares the test report for the exact fabric used in bulk production. This is the document your compliance team files.
What to ask your factory
Before you approve a UPF 50+ claim, ask these four questions:
- Can you share the lab test report for the bulk fabric — not a similar fabric, the actual one?
- Is the UPF rating inherent to the knit and dye, or does it rely on a finish that washes out?
- How does the rating hold up after repeated washing? Ask what the lab says about wash durability.
- Can the rating be printed on the hangtag and care label with the correct wording for my market?
A factory that answers all four with documents is a factory you can build a sun-protection line with. One that goes quiet after the first question is telling you something too.
How we handle UPF 50+ at Naditas
We work with UPF 50+ rated knit fabrics for our kids rash guards and can provide lab test reports with bulk orders. Our designers pair the fabrics with long-sleeve and high-neck options so the protection covers real skin area, and all-over sublimation prints are confirmed with strike-offs before production.