UPF vs SPF: What's the difference?

Alright, there’s quite a few acronyms going around here, so let’s start with the basics.

• SPF means Sun Protection Factor
  SPF is the rating system used for sunscreen. It measures how well a product protects your skin from UVB rays (the ones responsible for sunburn) when applied directly to skin.
  
• UPF means Ultraviolet Protection Factor
  UPF measures how much UV radiation passes through a fabric to reach your skin. And here's where it gets interesting: unlike SPF, UPF accounts for both UVA and UVB rays.
  
• What are UVA rays?
  Think A for ageing. UVAs are the ones that cause long-term skin damage and wrinkles. They penetrate deeply and can even slip through glass.
  
• What are UVB rays?
  Think B for burning. They’re the ones that cause immediate surface damage and are the main culprit behind a sunburn.

How is UPF measured and tested?

Testing involves exposing a fabric sample to UV radiation and measuring exactly how much passes through to the other side. From there, fabrics get classified into three tiers:

• 15–24: Good
• 25–39: Very Good
• 40–50+: Excellent

A few factors affect where a fabric lands. Weave tightness, fabric weight, colour and composition all play a role. Lighter or more loosely woven fabrics generally rate lower. And wet fabric can reduce UPF performance in some materials — which matters a lot in swimwear. (More on that in a second.)

Beyond the rating, how effective is UPF protection?

If you’re feeling a little skeptical about whether a piece of fabric can really outperform a liquid screen, the short answer is: it can.

Studies consistently show that UPF-rated fabrics provide significantly more UV protection than unrated clothing. Here's a number that surprises most people: a standard white cotton t-shirt has an approximate UPF of just 5. That's the kind of ‘protection’ most of us assumed was keeping us covered on beach days!

Compared to sunscreen, UPF clothing has a few distinct advantages: it doesn't wear off, doesn't need reapplying, and won't miss a spot. For long days in the water, outdoor workouts, or any situation where stopping to reapply is just not realistic — UPF fabric is a powerful option.

When is UPF swimwear worth it?

Not every situation calls for it, so let's be practical. UPF protection is worth prioritising when you're:

• Swimming in the ocean or pool (sunscreen washes off, UPF doesn't)
• Doing outdoor workouts under full sun
• Spending extended time on the water surfing, paddleboarding, or kayaking
• Travelling to high-UV destinations (hi, Australia — and yes, we know we live here)

It's also worth thinking about if you have sun sensitivity, a history of skin damage, or simply prefer not to rely entirely on topical SPF.

UPF 50+ at Sheila

Because we live under the intense Australian sun, UPF 50+ is Sheila’s baseline. Every single piece we make blocks approximately 98% of UV radiation. It’s the highest possible rating awarded, which means you’re getting maximum coverage the second you put it on.

But for swimwear, the real test happens in the water. While ordinary fabrics can lose their sun-blocking power when stretched or soaked, our premium recycled nylon holds its UPF 50+ rating completely intact, wet or dry.

Think of it as teamwork: liquid sunscreen still has a job to do on exposed skin, but with a UPF 50+ swimwear doing the heavy lifting, that’s one less thing to worry about. 

If you're looking for a little extra peace of mind and effortless coverage, our Alyssa , Miranda, and Cate  pieces are the perfect place to start.