It sounds counterintuitive, but the better a bike helmet vents, the heavier it will be. The holes and channels that move cooling air over your head require extra bulk to protect what's inside it. Giro's new Aeon uses a structural plastic shell that allowed designers to go all Biggest Loser on the inside without sacrificing comfort. We've put in several hundred miles in ours without wanting more airflow, yet the whole thing weighs just 7.9 ounces in a large.
WIRED Three-way customizable fit and barely there weight. Removable liner for washing.
TIRED Small adjustment knob is tough to dial with sweaty fingers. Priced for obsessives.