I have been known to ride during extremely hot weather (& so know full well how difficult it is to get 'melted asphalt' splatter off my Spyder! :shocked: ) and I have ridden both on and off the test tracks with just about all types of helmet with & without chin curtains, so I can say with some degree of confidence that (at least for me & everyone I know personally who has done/been subjected to the same type of testing!

) the helmet chin curtains on most quality helmets actually
DO help keep your head cooler; keep you more alert; and help reduce/delay the onset of heat & hydration issues!! So for me/my ryding, that's all good stuff that warrants keeping the chin curtains on all the time!

hyea:
Of course, your personal feelings & thoughts about this might vary, but I suspect that no matter how much you might '
feel' that taking the chin curtain off (or riding with a 1/2 or 3/4 helmet for that matter

) during hot weather might help you
think you're any cooler, actual testing of your temp & hydration levels are very likely to show otherwise :lecturef_smilie: But, as with so many other things, even if I & mine keep our helmet chin curtains on, it's your ride & your life, & just so long as you're not creating a hazard for others & those road users around you, you can fill yer' boots or whatever & do it your way! :thumbup:
After all, as someone once said (& my apologies to whom-ever for my subsequent corruption of their adage

)
It's not
WHAT you Ride (or wear!

) it's
THAT you Ride!

hyea: :2thumbs: