Nobody likes a whiteout that exists within their own goggles. Smith goggles, including the Phenoms, do have a great venting system that lets hot air escape easily, which works especially well when youre downhill skiing/riding, and your gogs are getting plenty of cool, refreshing airflow. But if you really want to amp up your ventilation during sweat-inducing aerobic activity, you should look into the Smith Phenom Turbo Fan Goggle. It has a tiny, quiet, battery-operated fan inside the goggle, and paired with Smiths standard anti-fog lens, this fan keeps things super-fresh and clear even when youre hot and sweaty. (You turn the fan on with a simple switch on the goggles elastic band.) Youre pretty much guaranteed to not have a fogging problem, and if youre worried about the fan breaking down at all, remember that Smith (and Backcountry) will back it up with a lifetime warranty.