This long-sleeve jersey is primarily designed to provide sun protection without weighing you down. The main body is a lightweight micro- polyester that offers plenty of airflow while providing UPF 50 protection. The sleeves are exceptional for a summer-weight sun-protection jersey, since they're very light and stretchy so they don't weigh you down while blocking 97% of UV rays (UPF 30). The Prologo 7 Long Sleeve is also a great jersey for cool spring and autumn days. With a heavier base layer you can take it down below 15degreesC/60degreesF, and then add a vest to go even colder.