I’m a big guy and I generate a lot of body heat. Plus, I live in Florida. So what’s the best fabric for staying cool?
Cotton!
Convince yourself. Get an old polyester suit and an old cotton suit at a thrift store.
Wear one out in the Florida sun for an hour or maybe 1/2 hour in the polyester and the change to the cotton. Wow what a relief and an hour in the cotton won’t be as bad as a 1/2 hour in the polyester.
In my experience, cotton.
For me it’s either cotton or silk. Natural fabrics on the whole are far superior to synthetics. But they’ve developed some specialized synthetic fabrics to be even more comfortable than natural cotton and silk. What’s this Coolmax stuff that’s been finding its way into my clothes? For activewear, nothing is better than Supplex at wicking away sweat and drying quickly. Great comfort. Supplex is lightweight, very soft, very comfortable, and dries way faster than cotton.
Not cotton. Linen. Silk retains heat, which is why aviators wore silk scarves and thermal underwear makers use it. Cotton is okay if nothing else is available, but the coolest fiber to wear, without doubt, is linen.
Of course, the trouble is that linen is expensive, hard to find, and wrinkles if you just look at it. On the plus side, once you start wearing it, it becomes softer and softer
Hemp.
If you sweat a lot (I do :eek: ) cotton sucks, it gets wet and stays wet!
The new high performance synthetics definitely keep me cooler and dryer! 
Nothing!
Become a nudist, but be careful of the sunburn.
If you don’t mind wearing Reebok/Nike, their Clima-Cool type fabrics are very comfy in hot weather. They can be kind of sheer, but you could always go for size larger than what you usually wear.
UnderArmor is nice for keeping you nice and dry, though not necessarily cooler.
Vote two for hemp. Hemp wicks moisture faster than cotton and evaporates off faster, doesn’t wrinkle as badly as linen, wears like iron and just gets softer and more comfy the more times it’s washed. It doesn’t mildew, and it floats, which is why it’s the fiber of choice for maritime use, sails don’t rot and the rope doesn’t sink. I have a pair of hemp hiking shorts I’ve been wearing for almost ten years, they get a ton of use and get washed once a week pretty much, still in excellent condition and only slightly faded.
Hemp/linen and hemp/silk blends are really nice too. The only downcheck to hemp is the cost.
Depends on which article of clothing. Cotton is best for a loose shirt. Coolmax is best for socks and breifs (cotton gets soaked with sweat and gets icky). For pants, again- cotton, although I have heard that hemp for jeans is OK, too.
Linen has it’s fans & detractors. It also needs to be a loose outergarment.
If you can’t wear synthetics, light thin wool is likely better for socks than cotton if you sweat a lot.
trendlon 
This. Cotton is definitely not cool in high humidity. Wear a pair of cotton jeans and a crew neck cotton T-shirt in the Florida summer and you will surely die. The key is to find performance synthetics in a button-down or V-neck pullover style which vents the heat and moisture instead of trapping it inside like a crew neck does.
(old thread but still relevant)
Polypropylene. I think there are more advanced materials now like microfibers, but this used to be the standard for cycling shirts. Usually what you read is that it wicks the moisture away from your body but I don’t know if that’s really the mechanism since I think it actually hydrophobic. However it works, it seems to do a pretty good job.
Well, it depends on the heat, the humidity and whether you wear it tight or loose.
Loose fitting linen is very cool. Wrinkles fast.
On your feet or underwear it’s a tie between wool or Coolmax, which is a special Polyester. Coolmax is cooler, but in my mind can make “crotch rot” worse. Smartwool and other companies make some very light weight wool underwear which breathes fantastically, is comfy, but does not have a long life if you machine wash it.
Cotton is much like Linen, in that if it’s loose it’s OK, but if you wear cotton tightly-whiteys or socks they get saturated with sweat fast and that’s not nice.
When I go to Disney world, I wear Smartwool boxers & sox, cotton shorts , and a linen shirt, or if I think it may rain, a light weight merino wool shirt, like Smartwool.
Hemp/cotton makes a decent jeans blend.
My vote goes for SeerSucker, those blue and whites the DownHome Southern Gentry wore.
Haven’t you ever heard of Fonzie? Clearly leather is what’s coolest!
Cotton is great until you start sweating. Then it sucks. Coolmax and similar technical materials are the best if you will be sweating as they wick away the sweat which then evaporates cooling your body down. That’s why us cyclists wear it. However you might now want to go around in skin tight lycra or jerseys all day. I don’t when I’m not riding or running!
But you can get shirts with Coolmax materials. Search Amazon for “HATHAWAY CoolMax” for an example. I use such a shirt to outdoor events in the summer especially after completely soaking a cotton shirt one time.
One further point: If you use any technical materials, such as Coolmax, follow the cleaning instructions carefully. Warm/hot water, machine drying, fabric softener, even drying sheets may ruin the wicking effect. I machine wash in cold water, gentle cycle with a ‘free’ detergent like Tide Free, then hang dry. It doesn’t take such materials very long to dry - overnight is long enough usually.
If you were a chick I could have contributed soooo much to this thread…even though I know nothing about fabrics and fashion.
sigh…
ignorance…
not…
fought…
today…
cough…
…go on…without me…
What’s the coolest fabric to wear?
Whatever I’m wearing.