UPF vs SPF: what the rating on sun protective clothing actually means

SPF rates sunscreen. UPF rates fabric. They sound like the same idea with a different letter, and they are not - they measure different things, in different ways, and only one of them keeps working at hour six.

If you have ever wondered why a sun-protective shirt does not have an SPF number on it, this is why.

SPF: a measure of time, on skin

SPF stands for Sun Protection Factor. It is a measure of how much longer protected skin can be exposed to UVB before it starts to burn, compared with bare skin.

Two things about SPF surprise people.

First, SPF is fundamentally about UVB - the wavelength that causes sunburn. UVA, the wavelength associated with skin ageing and which penetrates deeper, is not what the SPF number measures. That is what "broad spectrum" on the bottle is for, and it is a separate claim.

Second, the SPF you get is almost never the SPF on the label. Laboratory SPF testing applies sunscreen at 2mg per square centimetre of skin. Study after study finds that real people apply somewhere between a quarter and a half of that. Because the relationship is not linear, applying half the tested amount does not give you half the protection - it gives you considerably less. An SPF 50 applied the way most people apply it can behave more like an SPF 15.

Add sweat, water, and towelling off, and the number on the bottle becomes a best case you are unlikely to achieve.

UPF: a measure of transmission, through fabric

UPF stands for Ultraviolet Protection Factor. Rather than measuring time-to-burn, it measures a physical fact: what fraction of ultraviolet radiation passes through the fabric to reach your skin.

Crucially, UPF covers both UVA and UVB. It is not a UVB-only measure. A UPF rating is a statement about total ultraviolet transmission.

The Australian and New Zealand standard sorts fabric into categories:

  • UPF 15 to 24 - Good protection (blocks 93.3% to 95.9% of UV)
  • UPF 25 to 39 - Very good protection (blocks 96.0% to 97.4%)
  • UPF 40 to 50+ - Excellent protection (blocks 97.5% or more)

UPF 50+ is the top of the scale. It means the fabric lets through no more than 1/50th of the UV hitting it - blocking at least 98%.

The difference that actually matters

Here is the practical distinction, and it is the whole argument for covering up rather than creaming up.

Sunscreen degrades. Fabric does not.

An SPF 50 sunscreen is at its best in the first minutes after application and declines from there - it rubs off on your shirt, it sweats off, it breaks down in sunlight, and after two hours you are meant to reapply the whole lot. In practice, almost nobody does, especially not mid-round or mid-job. Golfers know this problem intimately - see why golfers burn even with sunscreen on.

A UPF 50+ fabric is exactly as protective at 4pm as it was at 9am. It does not need reapplying, it cannot be applied too thinly, and it cannot be missed in patches. You put it on once. There is no user error to make.

This is why dermatologists and cancer councils consistently put clothing first in the hierarchy of sun protection and sunscreen further down. Sunscreen is what you use on the skin you cannot cover.

Does washing or stretching ruin UPF?

It depends entirely on how the fabric earns its rating.

Some garments get their UPF from a chemical treatment applied to the surface. Those wash out. The rating is real when it is new and quietly declines with every cycle in the machine.

Better fabrics get their protection from the physical density of the weave. There is no coating to lose, so washing does not degrade it. IceRays sleeves are 85% Tactel and 15% Spandex - the protection comes from the weave itself, and the Spandex lets the sleeve stretch to your arm and recover its shape rather than being pulled open. (There is one laundry mistake that does cause damage, though - we cover it here.)

Ordinary clothing is a different story. A plain cotton t-shirt might offer a UPF of only 5 to 8 - and when it gets wet, that figure drops further, because water reduces the fabric's ability to scatter UV. That old white tee you wear to the beach is doing much less than you think. It is also why a sweated-through cotton shirt is a poor cover-up in the garden.

How to read a UPF claim without being fooled

The number is only as good as the testing behind it. Anyone can print "UPF 50+" on a label.

Ask who tested it. In Australia, the gold standard is ARPANSA - the Australian Radiation Protection and Nuclear Safety Agency, a government body rather than an industry group. When ARPANSA certifies a fabric, the result is verified by government scientists to the Australian and New Zealand testing standard.

For the record, IceRays fabric was measured at UVA transmittance of 0.000% and UVB transmittance of 0.000% - the "Excellent" category.

So which should you use?

Both, on different parts of you.

Cover what you can with tested fabric - it is the more reliable protection and it requires nothing of you after you put it on. Use sunscreen on what is left: face, ears, neck, the backs of your hands. And use a hat, because your scalp and the tops of your ears take a beating that no arm sleeve will help with.

The point is not that sunscreen is bad. It is that sunscreen depends on you applying it correctly, generously, and repeatedly - and fabric does not depend on you at all.

If you want that on your arms, our ARPANSA-certified UPF 50+ cooling sleeves slip on in seconds and hold their protection all day. Covered by 30-day returns.

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