How Can UPF Clothing Block Sunlight When the Clothing is See-Through?

Question

I see clothing that’s labeled UPF 50, but the clothing is basically transparent. The model’s bra shows through clear as day. How does such flimsy material block 98% of the sun’s rays?

In: Chemistry

Answer 1

UPF refers specifically to the ability to block UV light. Basically the material is transparent to visible light but not transparent to UV. The most common material we are familiar with that has those properties is glass, but there is no reason fabrics couldn’t.