When I bought a new Specialized SWorks helmet, it was expensive, but it was the first helmet I've ever worn where I forget that I'm wearing it. It was a *huge* improvement in airflow, comfort, and not trapping heat both when riding and when not riding.

The latest Specialized SWorks helmet is very different from the one I have though, so I'm afraid I'm not 100% sure what the current equivalent is. You can definitely get a helmet that you don't really get additional heat with it on for the bike though.