Originally Posted by
Beckdgc
Another thing to consider...
Helmets have a greater surface area than your head, so if properly designed the vents could be directing more air over your head than would otherwise hit your bare head. Whether or not that increased airflow(if it exists) + sun shading will overcome the insulating properties of the foam I don't know.
I won't say that any helmet could increase airflow compared to no helmet, but the "properly designed" part makes a big difference. I mentioned the Pneumo and S-Works helmets earlier and how the S-Works vented better. Looking at them now, I notice that the S-Works is basically a series of longitudinal ribs with air channels between them, while the Pneumo's channels are more convoluted. Wind coming through the S-Works basically has a straight shot from the front to the back.
I'd venture to say that since the airflow is so good, and how it's still deep enough to provide shade at most angles, it's at least as good as wearing a ballcap.
http://briko280.blogspot.com/2010/11/giro-pneumo.html
http://4.bp.blogspot.com/_A7QYCOUtiu...mo+White14.jpg
http://sprinterdellacasa.blogspot.co...ks-helmet.html
http://mountain.bike198.com/wp-conte...-s-works-6.jpg