How long does UPF last in sun protective clothing?
And, does UPF wash out of the clothing thus making it inefficient to block UV rays?
The answers are -- variable and sometimes. Because it depends on the type of fabric used and how the fabric was constructed.
Long before you put on your UPF clothing, the sun protection fabric was made in a textiles mill. And did you know there's different ways to make fabric sun protective?!
There are two ways to make fabric sun protective at the textiles stage of manufacturing: chemical and inherent.
Chemical sun protection is typically a topical finish or 'treatment' (a chemical UV filter) added to the last stages of producing fabric. For it to be labeled and rated sun protective, the finished textile must be tested and verified using industry standards such as AATCC TM 183 or AS/NZS 4399
Inherent sun protection means the sun protective factors actually become part of the fabric itself. The sun protective properties are woven into the fabric. This happens in the beginning stages of the textiles manufacturing process rather than at the end.
The best way to explain the inherent method is it is like having mineral sunscreen twisted into the fiber content, and those sun protective threads are then used to weave the fabric. The tightness of the fabric's weave (made with sun protective threads) also contributes to blocking UV rays.
It is important to note that the testing and UPF rating certification process happens when the fabric is brand new, never worn nor used.
So to answer your question,
Does UPF wash out of clothing made with fabric that's sun protective by chemical means? The answer is yes, eventually it will wash out. Additionally,
Chemical UV filters may break down over time and with continued exposure to the sun.
Does UPF wash out of clothing made with fabric that's made inherently sun protective? That answer is no, the sun protective properties will not wash out.
To be very clear, UPF clothing made with inherent sun protective properties permanent to the fabric will effectively sun protect your skin for the lifetime of the garment. When your garment's fabric itself wears thin from much use over time, you should replace it.
It will not wash out or lose its efficacy due to washing or constant time in the water, nor wear down from constant exposure to the sun.
As the consumer, it is difficult to know if you're purchasing UPF clothing or accessories made with fabric that's inherent or has chemical sun protective properties because it is not required to distinguish the method in which it blocks UVA and UVB rays.
If certified, the clothing will have a UPF rating only.
What to do?
When possible, search for sun protection clothing that's clearly labeled with a certified UPF rating inherent to the fabric. This movement towards transparency for the consumer is growing as consumers insist on knowing what they're buying and how it was made.
Brands serious about sun protective clothing will clearly state if the garment is made with permanent UPF that won't wash out.
Additionally, when possible look for sun protective clothing and accessories made with double certified fabric: a UPF rating and an OEKO-TEX Standard 100 rating.
This will ensure you are wearing clothing with no harmful chemicals touching your skin nor absorbing into your system.
It's also better for the environment.