Originally Posted by
CB HI
Depends on your choice of helmets and your riding speed.
Higher end helmets have more vents that are better designed to try to achieve a more laminar flow.
At very low speeds, neither a low or high end helmet gets much air flow. But then a bare head, at low speed does not get much air flow.
My experience is that a better helmet at >15 mph give more cooling and is about the same as a wetted skull cap.
Prior to climbs (slow speed), I just squirt a little water through the helmet vents to keep cool during the climb (make sure to use the bottle with water and not the one with sports drink).
Laminar flow is the opposite of what you want for cooling.
Also, I don't see any practical way that a helmet can convectively cool more than a bare head. All of the air flow in a helmet is coming from the free air stream around you. Air vent designs are basically a manifold that diverts that free air stream under the helmet and over your head. At best, this could achieve the same thing as a bare head, you get the free stream air velocity whooshing over your locks. At worst it loses most of the velocity to aerodynamic effects and friction and has a much smaller cooling surface area. The argument might have merit when you include shading with the helmet exterior acting as a big radiator. It couldn't radiate your own heat though because of the stryofoam.