I always wear this in a sunny day (white): https://www.underarmour.com/en-us/me...pid1257471-100
Yes, long sleeve!!! Just yesterday I participated in the NYC Gran Fondo, it was 29 degrees Celsius with 89% humidity and rode comfortably all day long. It not only helps me cool but its also rated 30 UPF. The science behind these technofabrics is amazing, they do work! I have tried adidas and nike versions, but UA is superior.