Leave it to Nike to come up with the coolest vest around—literally. The inner layer is filled with water and frozen overnight, and the cold is trapped with an outer layer of aluminum.
PreCool Vests were used by Olympians in Beijing, who wore it about an hour before competition to keep their body heat down in order to perform better. Unfortunately, the PreCool Vest won't be available to the hoi polloi (that means us), but we can look and admire, can't we?