>>2830541 (OP)
define "very hot". Hot and moist (tropics) or hot and dry (desert)?
What I use(d):
In the tropics:
>low fabric shoes (feiyue in my case)
>wide shorts in town, BDUs in the jungle
>merino shirt
>boonie
In dry heat (Western Germany lol - we get 40°C in summers most years):
>all-leather boots
>cargo shorts in town, cotton jeans in the forest
>merino shirt
>boonie or cheap straw hat
Also merino underwear, all the time. Having sweaty cotton rubbing your balls raw sucks.
>>2830542
Almost all of those are correct under some circumstances, but never all together.
>cover nape with t-shirt or cloth hanging from brimmed hat
Only in dry heat. in the tropics, it'll give you heatstroke. Not fun to experience.
>brimmed hat in general
Kinda. I'd suggest a boonie or slouch hat, though. Preferably made of linen or cotton, since that doesn't make you sweat as much. Get one that's a little big, so the air vents stay away from the head. Panama hats also kinda work, but get fucking expensive if you want the real thing instead of chinese straw (which'll rot in moist climate).
>shorts for airflow
Only in the tropics, and only if you don't need to worry about spiders and other crawlies. Wide, baggy, thin linen or cotton pants are better.
>natural fibers are even more essential when extra warm
Complete bullshit. Merino is pretty comfy, but nylon is just as good. Cotton always sucks (though it's at least bearable in dry heat), linen works in dry, warm climate, but gets uncomfy in extreme heat or wet weather. Hemp is like linen, but worse.