A long-sleeve rash guard beats any bikini for sun protection.

Yes, but the fabric rating matters less than how much skin you cover. UPF 50+ only blocks 98% of UVB rays on the areas the suit actually covers. A UPF 50+ bikini leaves your shoulders, back, and thighs exposed. That’s not maximum protection.

For maximum protection, you want coverage first: long sleeves, high neck, and ideally swim legg