The concept of a shirt with short sleeves escapes me. A lightweight fabric does the same thing, if it's really hot there's probably a lot of sun, so I don't expose more skin than absolutely necessary to it when wearing long sleeves. Plus, one can always roll them up if one really feels like it, it looks a lot cooler. If I need to wear a shirt, I probably need to wear a tie and jacket as well, so I short sleeves are not a choice. If I don't and it's really warm I go with a polo shirt.