What is UPF, and how is clothing tested?

What the rating means

UPF stands for ultraviolet protection factor. It is the sun rating for fabric, much as SPF is the rating for sunscreen, and it describes the material rather than the person wearing it. The Australian Radiation Protection and Nuclear Safety Agency, known as ARPANSA, puts it simply: the higher the rating, the more of the sun’s ultraviolet the material blocks, and the less reaches you.

A rating is a ratio. The laboratory compares the ultraviolet that reaches its sensor with no fabric in the way against the ultraviolet that reaches it through the fabric. Each wavelength is weighted by how strongly it acts on skin, so the shorter, stronger rays count for more. A fabric with a higher rating lets a smaller share of that weighted ultraviolet through.

The three bands

In Australia and New Zealand the rules sit in one standard, AS/NZS 4399:2020, Sun protective clothing: Evaluation and classification, published by Standards Australia in April 2020. It sorts fabric into three bands, and each band has its own words on the label: minimum protection, good protection and excellent protection. The top band holds two ratings, so there are four ratings in all, and ARPANSA notes that this system has stayed the same since the 2017 edition.

The bands are there to make a label easy to read. SunSmart, the sun safety programme in Victoria, and ARPANSA both point people who spend time outdoors to the excellent band. SunSmart also makes a fair point: fabric does not need a rating to stop the sun. A rating simply tells you that someone has measured it.

How a laboratory tests fabric

The test itself is quiet and precise. A small sample of fabric sits in a spectrophotometer, which passes ultraviolet light through it and measures what comes out, one wavelength at a time. The American method, AATCC TM183, works the same way and also reports how much UVA and UVB the fabric stops. It allows samples to be tested dry or wet, because water changes how some fabrics behave.

ARPANSA runs its own fabric laboratory, accredited by the National Association of Testing Authorities in Australia, and it issues reports under the 2020 standard. Those reports rate the material that was tested. They do not judge the design of the garment, or how much of the body it covers.

Why coverage counts too

A fabric can only cover the skin it sits on, so the standard has rules for the garment as well. ARPANSA explains that the 2017 revision introduced body coverage, and that the 2020 edition updated it. To carry a rating, a garment has to cover the upper body, including the torso and three quarters of the upper arm, or the lower body. Singlets, crop tops and briefs cannot make a sun protection claim, whatever their fabric.

Water, stretch and wear

A rating is measured on fabric in good condition. The label wording the standard asks for says that protection may be reduced if the material is wet, stretched, worn, or exposed to chemicals. ARPANSA adds that stretching a knit opens the spaces between its loops, and that many washes slowly fade and wear a garment.

Some testing tries to allow for this. The American practice ASTM D6544 ages fabric before it is measured, with rounds of laundering, simulated sunlight and chlorinated pool water, to stand in for two years of seasonal use. ASTM’s own summary is plain about why: the protection a textile gives is not fixed, and it changes over time.

What a rating leaves out

A rating is useful, but it describes one fabric, measured on one day, in a laboratory. It cannot tell you whether a cut pulls the knit open across your shoulders, or how the fabric looks after a summer of washing. For that, two simple checks help: hold the fabric up to the light, then try the shirt test with a UV card.

Where Rezzella stands

Every Rezzella piece is made to block the sun, and that is the only claim we make. Our fabric goes to ARPANSA, Australia’s radiation protection agency, for testing to AS/NZS 4399 before the first run. The full report goes on the shirt test page. Until then we print no rating anywhere.

That is also why every order comes with a UV card. Lay the Sun Hoodie or the Riviera Shirt over it in full sun, and you can see for yourself how much gets through.