I bought the Oakley Radar Path with dark lenses and no vent. Without the vent, the lens does get fog up easily and I have to remove it during mountain biking climbing. I decided to get the Persimmon Lens with vent for riding in the evening or fogging morning. The vent is perfect when you want to get the fog clear up while riding almost 90% of the time. If you are stationary and not moving, it does not help and still fog up. I decided to get additional Tungsten Lens which is darker for hot sunny day rides and also with vent. The vent does works when required and the fog clear up.