I live in the Pacific NW which has low humidity. I don't sweat when wearing the polyester jeans, unless it's above say 75 degrees. That's right, if it's a clear day and it's 60 degrees outside, my underwear does not get sweaty, even if I'm wearing polyester jeans. My problem is with my underwear getting wet from the rain. And if there is higher humidity on rainy days, well that doesn't make me sweat much either.

I'll look into athletic underwear at department stores.