I used to buy and wear bulky neckerchiefs that were filled with some absorbent that held a lot of water � enough for a day of work outdoors in nasty heat. The same outfit also had packets that you'd stash in your hat. Those gizmos really worked! Slow evaporation kept me cooler than I would've been without 'em.
I forget what they were called and where I got 'em. Gave a lot of 'em away, too.
When my old hunting partner A U Stanley was in Mexico breaking horses for General Pershing in the hunt for Pancho Villa, he wore a steeple-crown sombrero and kept a water-soaked sponge in its crown. Said he probably would've died without 'em.
