Kask helmets are rubbish for airflow imho, I have one and my head feels like its boiling in it and I sweat like a 80's BBC presenter with the police at the door
The Castelli headband imho is rubbish, I have one. The Castelli head thingy (it is the correct name) is far superior and more versatile, I have one for summer and a Castelli thermo head thingy for winter