Mississippi sumertime heat plus humidity and horseflies is pretty miserable. I can only handle early morning hikes to a creek to cool off then back to car. I don't think any cooling shirts or gadgets would make much difference. One thing I do is freeze water bottle so I have cold water. Mostly I just use treadmill at home and imagine I'm hiking in the mountains! I'm craving a trip to the mountains! Darn that Covid!!