During a real scorcher with high U.V.-index it's nice to wear a long-sleeved compression shirt with a nice application of Neutrogena Ultra Sheer Dry-Touch SPF 55 with helioplex spread underneath. Also, fill a large Camelbak bladder 2/3 full and freeze it into a solid block the night before. Fill the remainder with cold water before departing on a ride and you'll be rewarded with water chilled to 33* for hours.