they can be used.
personally i wouldn't bather bringing them though.
i bought them at DCA for WoC last year and my friend and i were about the only people wearing them which meant that they cool effect was not there.
i thought about bringing them to WDW last december but then didn't and i was glad cuz again nobody was wearing them even though they were for sale everywhere.
again this july going to WDW i did not bother to pack the bulky things and again i'm glad i didn't cuz only very few people were wearing them.