Not a valid experiment, More accurate would be to put the helmet on and go into a room at 100º F then stand in front of a fan. Then do the same with no helmet.
I just experienced this on my trip to Fl. and I have to tell you even my half helmet was torture compared to when I crossed the state line and could finally take the darn thing off. With the helmet off my sweat could evaporate thus cooling me the way the body was designed to cool itself. Not to mention the air flow over the area that the helmet had covered before.
I learned all I need to know about life by killing smart people and eating their brains. Eat right ,Exercise ,Stay fit, Die Anyway!
