A personal observation on outdoor clothing for mild activity, and not intended to get into the "cotton v.synthetic" controversy. I am an old fart, living on the Gulf coast of Florida. I have been a competative shooter for the last 30 or so years, and currently shoot several pistol and 3gun matches a month. June through August can be brutal, especially if the range is a sand pit, and relative humidity is high. I use Bullfrog 30spf on face and exposed skin, nylon shorts, boxers, cape back long sleeved DuPont "cool max or supplex" nylon flats fishing shirts, wide brimmed Dorfman Pacific vented hat, CamelBak, moisture wicking socks, and New Balance synthetic shoes. In an iced down cooler, 3 bottles of Gatorade (I'm a UF grad)couple of waters, and one of the cooling scarves with the water absorbing crystals. I can go through 70oz in the CamelBak and the EGR's in a typical match. Having access to the neck scarf and cold water for hat and bandana makes management of core body temp a little easier. I have a case of water and half dozen bottles of Gatorade in the car, and consume at least one during the hour drive home. regards Les

The general rule of thumb is that in moderate dry heat thin loose-fitting absorbent clothing holds sweat and allows evaporation to more efficiently cool you.

In high humidity you go with bare skin so the sweat falls off because it isn't going to evaporate.

If your in the sun a wide brimmed hat creates shade and light colored clothing absorbs less heat.

It all changes when heat goes well over 100F. At those temperatures the air is dry but extremely hot. So high that exposure to untreated air is harmful. In those conditions you see heavier insulating clothing that shroud the body and create a micro-climate like a space suit. Think of traditional Arab dress where the entire body is covered.

Of course in high heat you need to slow down. And many cultures stop work in the heat of the day. A work day that runs 0800 to 2000 with a four hour break from 1200 to 1600 can be quite effective in the summer when its daylight until 2100. I have also seen jobs run from 0500 to 1300. The long lunch system has the advantage that the crews essentially start fresh two time a day when energy and concentration are at their best.