Fit and seams matter most for a swim rash guard.

Yes—fit and seams. Everything else is secondary.

For long-distance open water swimming, your rash guard needs to be snug but not restrictive. Loose fabric creates drag and rubs you raw over hours. Flatlock seams are non-negotiable—they sit flat against the skin instead of digging in like standard overlocked seams. Check the inside of the sleeves and sides.

UPF 50+ is table stakes. You’re going to be in the sun for hours. If the fabric doesn’t have a UPF rating, it’s not a swim rash guard—it’s a regular shirt that will get heavy and saggy when wet.

Material matters: look for a blend of spandex and nylon or polyester. Pure spandex wears out fast with saltwater and chlorine. Nylon holds up better. Avoid cotton or any “rash guard” that feels soft like a T-shirt—that’s a sign it