Why did I sweat so much?

I am clearly the exception (it would seem) but here under shirts --- that are sweat proof -- seemed to increase my core temperature by 20-30 degrees. Ok - I am exaggerating but I was traveling by car and pulled over to take my shirt and tie off and rid myself of the undershirt so that I could cool down before my meeting. How? How does this work for others but makes me hot & sweaty. I bought two shirts and two underpants - I will say that the underpants seem better but truthfully I think the shirt experience sullied the whole deal.

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