I know hot is relative but here in central arkansas it can easily get to a 100 with 85% humidity, that is to hot to ride for all I care. I don't mind wearing my 661 until it gets to be over 93ish, I know that is a relatively specific number, but if it is much over that with the brutal humidity we have I won't ride anyway. If it is hot wear the suit by itself and it isn't that uncomfortable because it is made of mostly mesh and breathes well. When it gets around 70-75 I wear a jersey over it and couldn't be more comfy and that set up works to about 45-50 degree's for me. Much cooler and it is time for more layers.