Our most technical sun protection layer is designed for breathability and durability, making it ideal for long, sweaty, multi-day treks where built-in sun protection is critical | The highly abrasion-resistant, stretchy, UPF 50+ fabric and low-bulk bonded seams are strategically constructed so they can withstand hours of pack rub without breaking down | Bottom line: if you only carry one shirt, make sure it's Olia.