What UPF 50 means, in plain words
UPF tells you how much of the sun gets through your clothes. Here is how to read the number and what changes it.
The short answer
UPF stands for Ultraviolet Protection Factor. It is a measure of how much of the sun's ultraviolet light gets through a fabric. UPF 50 means about one fiftieth of the UV gets through. The other 49 parts are blocked.
How the ratings are grouped
In Australia and New Zealand, clothing is rated under the standard AS/NZS 4399:2020. ARPANSA, Australia's radiation protection agency, groups the ratings like this:
| Rating | Category |
|---|---|
| UPF 15 | Minimum protection |
| UPF 30 | Good protection |
| UPF 50 and 50+ | Excellent protection |
Source: ARPANSA
UPF is not SPF
SPF is for sunscreen and is tested on skin. UPF is for fabric and is tested in a lab with a spectrophotometer. Both tell you how much UV gets past, but they are measured in different ways, so you can't swap one number for the other.
What changes a fabric's UPF
- Weave. A tight weave leaves fewer gaps for light.
- Fibre. Some fibres absorb more UV than others.
- Colour. Darker and brighter dyes tend to absorb more UV.
- Stretch. Stretching opens the weave and lets more through.
- Water and wear. Wet or worn fabric can protect less.
Why we pay for a lab
You can't see UV, and you can't judge a fabric by holding it up to a window. That is why we send every fabric to ARPANSA and publish the result. Until the result is back, we make no claim. See our proof page