It works better in the shade, and best of all in the shade exposed to a breeze. You don't need to warm the water in the rag to evaporate it. It will evaporate i

It works better in the shade, and best of all in the shade exposed to a breeze. You don't need to warm the water in the rag to evaporate it. It will evaporate in the dry air, even if cool. Putting it in the sun raises its temperature as the evaporation lowers it. If there's a nice breeze, evaporation will still win, but it will get cooler if you don't add energy at the same time you are removing it.