never let them see you sweat

please explain this one to me. why on earth are many frum brooklyn women wearing sweater in the 95 degree weather that we are having and  they aren't passing out from the heat? i am not wearing a 'summer sweater' and i  feel like im swimming in perspiration. i  can barely move. i don't get it. they don't even seem to be sweating , even those who are wearing shaitels. how is this possible?
all i can say is wake me up when its september when the weather is  less oppressive.


p.s. the above photo was taken in september 2009.