You'll also notice that it's loose-fitting cotton, not hot leather or nylon. I'm sorry, but I've worn a full-face helmet in 100 degree weather, and I did not feel any cooler.
No one said you would feel cooler, just that you would not feel hotter.
and that is a stretch anyway, as the point is to keep you from cooking or dehydrating.
Case in point, Did a 150 mile ride with ambient temps in the high 90's . Wore a t-shirt, thin cotton pants, tennis shoes and a 3/4 helmet with no shield , but goggles.
Got to my destination and felt like crap for a good 3 hours.
Fastforwad to the same trip, same tempatures, but me with a windscreen, FF helmet, mesh pants and jacket...no exposed skin other than my neck.
Got there and felt great.
On both trips
...I still felt like I was being baked...but when I finally stopped, my recovery time was almost instant with all the mesh gear, and without it I actually felt kinda worn out and sick.
HOT is HOT and other than taking the air conditioned car, you ain't going to feel "cool". What you are working for here is not getting overheated badly... or sick, or suffering long term effects of being in that heat.