Bullshit. I've worked under extreme conditions, probably about as long as you've been alive, and have the experience to back up my claims. Polyshit makes you hotter, period, end....
I second this, except for the length of time.
I work as a lan/computer tech for a factory. We are lucky that we have large a/c units to help cool the floor. when they are working and the doors are kept closed.
on days its not and hot out, it gets hot inside. It gets really hot in the jacketing area. (we make cable)
I have some 50/50 cotton polyester shirts and i hate them. thankfully the dress code is light here for me because mostly i were 100% cotton t-shirts with the company log on them and they are much, much cooler. I also stooped tucking my shirt in. It helps let air flow through and evaporate the sweat from your skin. Even in the 50/50 shirts it helps, when there is a breeze.
Maybe those form fitting bicycle cloths work differently because they are right on your skin, but average cloths, no, i don't want anything to do with anything with synthetic material that touches my skin.
As for advice on how to try and keep cool, all i have to do is keep working and try not to think about it. But i also have the luxury of coming back to our a/c office.
Edit: oh and yes, 110f or 43c is very doable in most factories. Add working with something that generates a lot of heat and it will get hotter.