All clothing protects you from the sun to some extent. UV protective clothing, however, has a specific, protective scale not unlike sunscreen. A lot of UV protective clothing actually contains sunscreen in the fabric itself. Some garments are said to be UV protective due to their weave, color, and/or reflective nature.
SPF and UPF are acronyms you will see as you look into UV protective clothing. SPF stands for “sun protection factor,” and it’s what you see on lotion, sunscreen, and other topical protectors. SPF is measured by how long it takes your skin to turn red in the sun.