Ive just come back from a 6 day 30c plus (last two days 35c, humidity 28%) trip wearing an Icebreaker Tech-t 150 top.
I developed prickly heat under both armpits.
The only time I had prickly heat before was years ago whilst working up in Dawin for a couple of years. Same spot, armpits.
The top was moist for most of the day, but not excessively so...except for the back...Golites Pinnacle pack doesnt have much in the way of airiness. Pack did not contact the armpits, and their was some space for breathing between the pack and the armpits. My back had no prickly heat/rash.
After much deliberation all I can track it to is the fact that high humidity and my armpits dont mix.
Its a shame the wool tops dont evaporate the moisture so well as other tops.
Im happy the girlfriend has a sewing machine...time for some vents in the tech-t to be installed